Daily Interest Calculator
Savings & BankingInterest that accrues day by day.
Balance, rate & days
Interest is added every day, so it starts earning interest of its own.
The denominator that turns the annual rate into a daily rate. A 360-day year makes each day worth a little more.
Advanced options
- Starting balance$10,000
- Interest$513
These figures are estimates for planning only and assume the rate and settings hold for the whole period. They are not financial, banking, investment, legal, accounting or tax advice. Your bank's real day-count method, crediting schedule and rounding may differ.
Simple vs compound interest
The same 0.0137% daily rate over 365 days, earned two ways.
- Simple interest$500
- Compound (daily)$513
Daily compounding earns $13 more — interest landing on interest.
Balance over time
Compare scenarios
Ending balance under different tweaks, over 365 days.
- Your plan$10,513
- +1% rate$10,618
- Simple interest$10,500
- Twice as long$11,052
Day-by-day accrual
Grouped into periods — 365 days is too many rows to list one by one.
| Days | Deposit | Interest | Interest to date | Balance |
|---|---|---|---|---|
| 1–6 | — | $8 | $8 | $10,008 |
| 7–12 | — | $8 | $16 | $10,016 |
| 13–18 | — | $8 | $25 | $10,025 |
| 19–24 | — | $8 | $33 | $10,033 |
| 25–30 | — | $8 | $41 | $10,041 |
| 31–36 | — | $8 | $49 | $10,049 |
| 37–42 | — | $8 | $58 | $10,058 |
| 43–48 | — | $8 | $66 | $10,066 |
| 49–54 | — | $8 | $74 | $10,074 |
| 55–60 | — | $8 | $83 | $10,083 |
| 61–66 | — | $8 | $91 | $10,091 |
| 67–72 | — | $8 | $99 | $10,099 |
| 73–78 | — | $8 | $107 | $10,107 |
| 79–84 | — | $8 | $116 | $10,116 |
| 85–90 | — | $8 | $124 | $10,124 |
| 91–96 | — | $8 | $132 | $10,132 |
| 97–102 | — | $8 | $141 | $10,141 |
| 103–108 | — | $8 | $149 | $10,149 |
| 109–114 | — | $8 | $157 | $10,157 |
| 115–120 | — | $8 | $166 | $10,166 |
| 121–126 | — | $8 | $174 | $10,174 |
| 127–132 | — | $8 | $182 | $10,182 |
| 133–138 | — | $8 | $191 | $10,191 |
| 139–144 | — | $8 | $199 | $10,199 |
| 145–150 | — | $8 | $208 | $10,208 |
| 151–156 | — | $8 | $216 | $10,216 |
| 157–162 | — | $8 | $224 | $10,224 |
| 163–168 | — | $8 | $233 | $10,233 |
| 169–174 | — | $8 | $241 | $10,241 |
| 175–180 | — | $8 | $250 | $10,250 |
| 181–186 | — | $8 | $258 | $10,258 |
| 187–192 | — | $8 | $266 | $10,266 |
| 193–198 | — | $8 | $275 | $10,275 |
| 199–204 | — | $8 | $283 | $10,283 |
| 205–210 | — | $8 | $292 | $10,292 |
| 211–216 | — | $8 | $300 | $10,300 |
| 217–222 | — | $8 | $309 | $10,309 |
| 223–228 | — | $8 | $317 | $10,317 |
| 229–234 | — | $8 | $326 | $10,326 |
| 235–240 | — | $8 | $334 | $10,334 |
| 241–246 | — | $8 | $343 | $10,343 |
| 247–252 | — | $9 | $351 | $10,351 |
| 253–258 | — | $9 | $360 | $10,360 |
| 259–264 | — | $9 | $368 | $10,368 |
| 265–270 | — | $9 | $377 | $10,377 |
| 271–276 | — | $9 | $385 | $10,385 |
| 277–282 | — | $9 | $394 | $10,394 |
| 283–288 | — | $9 | $402 | $10,402 |
| 289–294 | — | $9 | $411 | $10,411 |
| 295–300 | — | $9 | $419 | $10,419 |
| 301–306 | — | $9 | $428 | $10,428 |
| 307–312 | — | $9 | $437 | $10,437 |
| 313–318 | — | $9 | $445 | $10,445 |
| 319–324 | — | $9 | $454 | $10,454 |
| 325–330 | — | $9 | $462 | $10,462 |
| 331–336 | — | $9 | $471 | $10,471 |
| 337–342 | — | $9 | $480 | $10,480 |
| 343–348 | — | $9 | $488 | $10,488 |
| 349–354 | — | $9 | $497 | $10,497 |
| 355–360 | — | $9 | $505 | $10,505 |
| 361–365 | — | $7 | $513 | $10,513 |
How it's calculated
- The 5.00% annual rate ÷ 365 days gives a daily rate of 0.0137%.
- Each day the balance earns that rate and the interest is added, so the next day's balance earns a little more.
- Over 365 days that adds up to $513 of interest.
- The ending balance is $10,513.
Know what this estimate is based on
- Jurisdiction
- General mathematical model
- Scope and limitations
- Projection only. Actual APY, posting dates, compounding, taxes, withdrawal rules, deposit protection, and fees depend on the financial institution and country.
- Source links checked
- Jul 30, 2026
Built and regression-tested by Smart Tools Lab. It has not been individually reviewed by a licensed financial, tax, or legal professional.
How to use
- 01
Pick a mode: choose what to solve for — interest earned, or reverse-solve for the required annual rate, the starting balance, the recurring deposit, or the number of days needed to reach a target ending balance.
- 02
Enter your starting balance — the principal the daily clock begins from (the default example uses $10,000).
- 03
Choose the interest type and rate: switch between simple and daily-compound accrual, then enter the annual rate, tagging it as APR (nominal) or, for compounding only, as APY (effective, which ignores the basis).
- 04
Set the day-count basis and horizon: pick actual/365 or actual/360 as the daily-rate denominator, then enter the number of days, up to 3,650 (ten years).
- 05
Optionally open Advanced to add a recurring deposit (daily, weekly, biweekly, or monthly), a tax rate applied to interest, and an inflation rate to reveal the real, today's-money value.
- 06
Read the results: the daily rate and annualized yield, total interest and ending balance, the side-by-side simple-versus-compound comparison, and the day-by-day table you can print or scan.
Formula
Daily rate APR mode: dailyRate = APR / basis (basis = 365 or 360) APY mode (compound): dailyRate = (1 + APY)^(1/365) - 1 (basis ignored) Interest over N days Simple: interest = P * dailyRate * days ending = P + interest Compound: ending = P * (1 + dailyRate)^days interest = ending - P Annualized yield Compound: yield = (1 + dailyRate)^365 - 1 Simple: yield = dailyRate * 365 Tax and inflation afterTaxInterest = grossInterest * (1 - taxRate) (tax swept yearly + final day) endingAfterTax = P + afterTaxInterest realValue = endingAfterTax / (1 + inflation)^(days/365) Legend P = starting balance (principal); APR = nominal annual rate; APY = effective annual rate; basis = day-count denominator (365 actual/365, 360 actual/360); days = horizon in days; taxRate = annual tax on interest; inflation = annual inflation rate. Note: the annualization exponent is always 365 calendar days, so an actual/360 quote yields more than its nominal figure. Recurring deposits post at day-end and earn from the next day.
Example
Start with $10,000 at 5% APR, compounding daily on an actual/365 basis for one year. The daily rate is 5% / 365 = 0.0137% (0.013699% carried to full precision), so the very first day earns $10,000 x 0.013699% = $1.37. Because each day's interest joins the balance and begins earning the next morning, the daily amount creeps upward and averages about $1.40. After 365 days the balance reaches $10,512.67, a total of $512.67 in interest, and the effective annual yield works out to 5.127% (5.1267%) rather than the headline 5%. Run the same money as simple interest and the daily figure stays pinned at $1.37 all year, producing exactly $500.00 and an ending balance of $10,500.00; the $12.67 difference is purely the reward for letting interest compound. The day-count basis matters too. Quote 6% on an actual/360 basis and the daily rate becomes 6% / 360 = 0.0167% (0.016667%), yet interest still accrues across all 365 calendar days. That lifts the yield to 6.272% (6.2716%) and pays $627.16 over the year instead of the $600.00 a plain 6% implies. The extra $27.16 is the actual/360 kicker.
Definitions
- Daily interest rate
- The annual rate cut down to a single day's slice. In APR mode it is the rate divided by the day-count basis; this per-day figure is the one multiplied against your balance every single day.
- Day-count basis
- The denominator that turns an annual rate into a daily one, either 365 (actual/365) or 360 (actual/360). It changes the daily rate but never the 365-day exponent used to annualize.
- Actual/360
- A banker's-year convention that divides the annual rate by 360 yet still accrues interest across all 365 calendar days. The realised yield therefore runs above the quoted nominal figure by a small kicker.
- Simple interest
- Interest figured on the original principal alone. Each day earns the same fixed amount because interest already earned is set aside and never itself starts to earn, so the daily amount stays flat.
- Daily compounding
- Interest added to the balance at the close of each day, so from the next day onward it earns interest too. Because the base keeps growing, the daily interest amount climbs steadily over the run.
- APR
- The annual percentage rate quoted as a nominal figure. It is split into equal daily pieces by the day-count basis and, on its own, says nothing about how often the interest actually compounds.
- APY / effective annual rate
- The genuine yearly return once compounding is folded in. Entered as APY, the daily rate becomes (1+APY)^(1/365)−1, and a full 365-day compound run returns exactly the APY you entered.
- Accrued interest
- Interest that has built up on a balance but has not yet been paid out separately. This tool tracks it day by day and, under compounding, rolls it into the balance at the end of each day.
- Annualized yield
- The one-year equivalent of the daily rate: (1+dailyRate)^365−1 when compounding, or dailyRate×365 when simple. It lets a per-day figure be compared directly against ordinary annual rate quotes.
- Recurring deposit
- A fixed sum added on a chosen cadence — daily, weekly, biweekly, or monthly. It posts at the end of the day and starts earning the next, so one year holds 365, 52, 26, or 12 of them.
- Real value
- The after-tax ending balance restated in today's money. It is found by deflating that balance over days divided by 365 years at your inflation rate, showing purchasing power rather than the headline dollar total.
- Crediting frequency
- How often earned interest is applied back to the balance. On this daily clock, compounding credits every day, whereas simple interest never credits back into the principal that is doing the earning.
Good to know
Two numbers describe daily interest
Every daily-interest question comes down to two figures, and once you can read both you can read any statement. The first is the daily rate: the slice of your annual rate that lands on the balance each single day. The second is what a stretch of days actually earns, which is simply that daily slice replayed across the horizon and, in the compounding case, folded back in as it goes. Take the reference run of $10,000 at a 5% APR compounded daily over 365 days. The daily rate works out to 0.0137% (0.013699% at full precision), a number so small it looks like rounding noise. Applied once, it turns that $10,000 into $1.37 of first-day interest. That single dollar and change is the whole engine. Replay it for a year and the earnings stack to $512.67 in total interest, lifting the ending balance to $10,512.67. Notice the two figures are not the same kind of thing. The daily rate is a fixed property of the account, unchanging from the first morning to the last. What a period earns is cumulative and, under compounding, mildly accelerating: the first day pays $1.37, yet the run averages $1.40 across all 365 days because later days work on a slightly larger balance. Hold those two numbers apart in your mind and the rest of this tool becomes legible. The daily rate tells you how hard each dollar works per day; the period total tells you what that effort adds up to. Confusing them is the classic error, treating a headline APY as though it were a daily figure or reading a day's pennies as the annual result. Keep the rate and the earnings distinct, and every disclosure, projection, and reverse calculation on the following pages falls into place cleanly.
Simple versus daily compounding mechanics
The signature choice in this calculator is the accrual style, and the difference is mechanical rather than cosmetic. Under simple accrual, interest is earned on the starting balance alone. Earned interest is set aside and never itself earns, so the daily interest amount is a flat, unchanging figure from the first day to the last. Under daily compounding, each day's interest is added back to the balance, and from the next morning it earns alongside the original principal. Because the base it works on grows, the daily interest amount climbs, slowly at first and then with visible momentum over long horizons. The reference numbers make the gap concrete. Run $10,000 at 5% for 365 days under simple accrual and you collect exactly $500.00 of interest, for an ending balance of exactly $10,500.00. Run identical inputs under daily compounding and you collect $512.67, ending at $10,512.67. The daily-compounding advantage is $12.67, and every cent of it is interest that has itself earned interest. Over a single year the effect is modest, but it is the same mechanism that dominates long-run outcomes, and it grows faster as horizons lengthen and rates rise. Why does compound pull ahead? Because simple accrual leaves each day's interest idle while compounding puts it straight back to work. The starting balance does identical labour in both styles; the divergence is entirely about what happens to the interest once earned, idle in one case, re-employed in the other. This is also why the daily amount stays constant under simple accrual and rises under compounding: a fixed base yields a fixed daily figure, while a growing base yields a growing one. Choosing between the styles is really choosing whether your earned interest sits still or gets back to work each day, and over long spans that choice decides the outcome.
The daily rate formula piece by piece
The pivot output of the whole tool is the daily rate, and in APR mode it is built from two parts you can inspect separately. The formula is dailyRate equals APR divided by basis. The APR is your nominal annual rate, the headline percentage a bank quotes. The basis is the day-count denominator, either 365 or 360, and its only job here is to convert that annual figure into a per-day figure. Nothing more elaborate is happening: you are slicing one year's nominal rate into daily portions. Feed in 5% APR on a 365 basis and the division yields 0.0137%, or 0.013699% carried to full precision. That is the number applied to the balance each day. Change the APR and the daily rate moves in proportion; change the basis and only the denominator shifts. Because the relationship is a plain division, the daily rate scales linearly with the quoted APR, which is exactly why reverse solving for a required rate behaves so well later on. It helps to separate two ideas the word rate tends to blur. The APR is an annual quote, a promise about a full year. The daily rate is the working number, the actual multiplier that touches your money between one day and the next. The basis is the bridge between them, and choosing 360 instead of 365 makes each daily slice slightly larger because you are dividing the same annual rate into fewer parts. Simple accrual always reads the entered rate as a nominal APR through this same division; there is no effective-rate option in simple mode, because flat interest has nothing to compound. Understanding the three pieces, APR on top, basis underneath, and the daily rate as the quotient, demystifies the pivot number that drives every projection the calculator produces from the first day onward.
Why actual/360 quietly yields more
The day-count basis looks like a footnote and behaves like a lever. Your only choices are actual/365 and actual/360, the second nicknamed the banker's year, and the basis is purely the denominator that turns an annual rate into a daily one. Here is the subtlety that catches people out: the basis divides the rate, but it does not shorten the year. Interest still accrues on every one of the 365 calendar days, and the annualization exponent is always 365 regardless of which basis you pick. So choosing actual/360 divides your rate into fewer, fatter daily slices and then applies those fatter slices across a full 365-day year. The result is a yield quietly above the nominal quote. The reference case shows the size of the effect. Take 6% APR compounded daily on $10,000 under actual/360. The daily rate becomes 0.0167% (0.016667%), noticeably larger than the same 6% would give on a 365 basis. Run it for 365 days and the annualized yield reaches 6.272% (6.2716%), delivering $627.16 of total interest rather than the $600.00 a plain 6% suggests. That extra $27.16 is the actual/360 kicker, and it is not an error or a bonus, it is the arithmetic of dividing by 360 while accruing over 365. Lenders have long favoured actual/360 on money they lend precisely because it lifts effective yield above the stated rate without touching the headline. When you are earning, the same convention works mildly in your favour; when you are borrowing, it works mildly against you. Either way, read the basis before you compare two quotes. Two accounts advertising the same nominal APR can pay materially different amounts once you know one runs on 365 and the other on the banker's 360.
APR versus APY and the round-trip
APR and APY answer different questions, and this calculator lets you enter either, so it pays to know which you are holding. APR is a nominal annual rate: a headline figure that, in APR mode, is simply divided by the basis to produce the daily rate. APY is an effective annual rate: it already accounts for compounding, describing what a full year actually returns rather than what the quote nominally promises. In APY mode, which is available for compounding only, the daily rate is found by taking one plus the APY to the power of one over 365, then subtracting one. Crucially, the basis is ignored in APY mode, because an effective annual figure annualizes over 365 days by definition. The clean test of consistency is the round-trip. Enter 5% APR compounded daily over 365 days on $10,000 and you earn $512.67, which corresponds to an annualized yield of 5.127% (5.1267%) once daily compounding is counted. Now go the other direction: enter 5% as an APY on the same $10,000 for 365 days. The daily rate drops to 0.0134% (0.013368%), and a full year earns exactly $500.00, ending at exactly $10,500.00. It round-trips precisely to the entered APY, which is the whole point of the effective figure, it is the number you actually receive after compounding, not before. Simple accrual has no APY option, because flat interest never compounds and its effective and nominal rates are identical: 0.013699% per day times 365 is a clean 5.000% either way. The practical lesson is to compare like with like. Set two accounts side by side on APY and you are comparing true annual returns; compare them on APR and you must still account for how often each one compounds before the numbers mean anything at all.
Recurring deposits on a daily clock
Most real accounts are not static, so the calculator lets you add recurring deposits and runs them against the same daily clock as the interest. You choose a cadence, daily, weekly, biweekly, or monthly, and each deposit posts at the end of its day and begins earning the next morning. That one-day lag matters over long horizons and is modeled explicitly rather than glossed over. The cadence maps to a predictable count across a year: daily gives 365 deposits, weekly 52, biweekly 26, and monthly 12, where monthly is modeled as a fixed 30-day interval rather than a calendar month. Working in fixed 30-day steps keeps the daily engine consistent and avoids the ragged month-length problem, at the small cost of not tracking specific calendar dates. The reference case shows deposits and compounding working together. Start with $10,000, add $100 every week at 4% APR compounded daily over 365 days. Fifty-two deposits arrive, contributing $5,200 of your own money. Interest across the year totals $511.73, and the ending balance settles at $15,711.73. Notice that the interest figure reflects both the original principal and the growing stack of deposits, each of which starts earning the day after it lands and compounds from there. Earlier deposits earn for nearly the full year; the final deposit of the run earns almost nothing, because it posts near the end and has scarcely any days left to work. This is why deposit timing, not just deposit size, shapes the result. A daily cadence puts money to work sooner than a monthly one for the same annual total, so it earns marginally more. When you compare savings plans, look past the headline contribution and ask how often the money actually arrives, because on a daily clock, sooner is always slightly better than later.
Tax and inflation on daily interest
Interest you earn is rarely all yours to keep, and money you keep is rarely worth what it says on the ledger. This calculator handles both erosions in sequence so the ending figure reflects reality rather than the gross headline. Tax is applied to interest only, swept once a year and again on the final day, and the balance the tool reports is after-tax. Inflation is then applied on top, deflating that after-tax ending balance into today's money over a span of days divided by 365 years. The order matters: tax reduces the dollars you hold, and inflation restates whatever survives in terms of present purchasing power. The reference case runs both at once. Put $10,000 at 5% APR compounded daily for 730 days with a 22% tax rate and 3% inflation. Gross interest across the two years comes to $1,045.85. Tax claims $230.09 of that, leaving after-tax interest of $815.76 and an after-tax ending balance of $10,815.76. Then inflation does its quieter work: expressed in today's money, that balance is worth $10,194.89. The gap between $10,815.76 and $10,194.89 is not a fee anyone charged you, it is the erosion of purchasing power over two years, and ignoring it flatters every long-run projection. Reading the three figures together tells the honest story. The gross interest shows what the rate produced. The after-tax balance shows what the taxman left. The inflation-adjusted figure shows what that money can actually buy when you finally spend it. A nominal gain can look healthy and still lose ground in real terms if inflation outpaces the after-tax return. Keeping tax and inflation in view separates a return that merely looks good on paper from one that genuinely grows what your savings can command in the shops.
Reverse solve modes as planning tools
Most of the time you run the calculator forward: enter the inputs and read the ending balance. But planning usually starts from the goal, not the inputs, which is why the tool inverts itself into four reverse modes. Instead of asking what a set of inputs produces, each mode fixes a target ending balance and solves for the one unknown you care about. You can solve for the required annual rate, the required starting balance, the required recurring deposit, or the number of days needed to reach your target. Two reference cases show the modes in action. Suppose you hold $10,000 and want $11,000 in exactly 365 days under daily compounding; the calculator solves for the rate and returns a required 9.53% APR. That single number tells you at a glance whether your goal is realistic: if no account on the market pays near 9.53%, you know to adjust the target, extend the horizon, or add deposits. The second case fixes the rate and solves for time. Grow $10,000 to $10,500 at 5% APR compounded daily and the tool reports 357 days, a touch under a full year, which squares with the earlier result that a full 365 days at 5% earns $512.67, comfortably past the $500 mark. Each reverse mode isolates a lever you might actually control. Rate solving benchmarks the market you need. Starting-balance solving tells you the lump sum a goal demands up front. Deposit solving turns a target into a savings cadence. Day solving tells you how long patience must last. Because the underlying daily engine is the same in both directions, a forward run and its matching reverse run always agree, so you can move fluidly between what will this produce and what do I need without leaving the tool.
Reading a bank's daily-interest disclosure
Once you understand the engine, a bank's daily-interest disclosure stops being opaque and becomes a short checklist. Three details govern what you will actually be paid, and they are easy to find if you know their names. The first is the distinction between compounding and crediting. Many accounts accrue interest daily but only credit it to your balance monthly or quarterly. If interest compounds daily, each day's earnings join the balance and start working the next morning, exactly the mechanism that turns $10,000 at 5% into $10,512.67 over a year rather than a flat $10,500.00. If interest is merely accrued daily but credited monthly, the compounding is coarser and the yield sits closer to the simple result. Read which word the bank uses. The second detail is the day-count basis. An account on actual/360 divides the annual rate into fatter daily slices while still paying across all 365 days, which is why a 6% quote on that basis returns $627.16 rather than $600.00, an extra $27.16 that never appears in the headline. Always check whether a quote runs on 365 or 360 before you set it beside another. The third detail is rounding. Real institutions round the daily interest amount, often to the cent, and small rounding conventions compound over hundreds of days into differences worth noticing on large balances. This calculator carries full precision, so treat its output as the clean benchmark and expect a bank's actual postings to drift by pennies. Finally, ask whether the rate is fixed or promotional, because this tool assumes a single steady rate, so a teaser that expires will make reality fall short of the projection. Compounding frequency, day-count basis, and rounding are the three questions that turn a marketing rate into the number you will really receive.
The default example end to end
It helps to walk the flagship example from start to finish, because it exercises nearly every idea in the tool at once. The inputs are the default set: $10,000 of starting balance, a 5% APR, daily compounding, a horizon of 365 days, and no deposits, tax, or inflation. First the calculator derives the daily rate by dividing the 5% APR by the 365 basis, giving 0.0137%, or 0.013699% at full precision. Apply that to $10,000 and the first day earns $1.37. Because compounding folds each day's interest back in, the daily amount edges upward, so across the year the run averages $1.40 per day even though it began at $1.37. Add up all 365 days and the total interest is $512.67, lifting the ending balance to $10,512.67. The annualized yield this daily compounding produces is 5.127%, or 5.1267% carried further. Set that against the simple-accrual version of the identical inputs, which earns a flat $500.00 and ends at $10,500.00, and the daily-compounding advantage is exactly $12.67, the interest that earned interest. Now hold the horizon and balance fixed and switch the basis to see the day-count effect. At 6% APR compounded daily on actual/360, the daily rate rises to 0.0167% (0.016667%), the annualized yield climbs to 6.272% (6.2716%), and the year returns $627.16 instead of the $600.00 a plain 6% implies, an extra $27.16 delivered by the banker's year. Read side by side, the two runs teach the whole tool: the daily rate is the pivot, compounding is what makes the daily amount grow, and the basis quietly reshapes the yield beneath the headline rate. Every other feature, deposits, tax, inflation, and the reverse solvers, layers onto this same daily clock.
Frequently asked questions
What does "daily interest" actually mean?
Daily interest is interest worked out on a true day-by-day clock rather than once a month or once a year. Each day the calculator takes your balance, applies that day's rate, and records the interest earned. On $10,000 at 5% APR compounding daily, the first day earns $1.37, and across 365 days the interest totals $512.67, ending at $10,512.67. The average works out near $1.40 a day. Running the clock daily is what separates this tool from calculators that only tick monthly or annually.
What is the difference between simple and daily-compounding accrual?
Simple accrual pays interest on your starting principal only; earned interest never earns anything itself, so the daily interest amount stays flat. Daily compounding adds each day's interest back to the balance, so the next day it earns too, and the daily amount slowly grows. On $10,000 at 5% for 365 days, simple interest is exactly $500.00 (ending $10,500.00), while daily compounding reaches $512.67. The $12.67 gap is the daily-compounding advantage — small over one year, larger over longer horizons.
How is the daily rate calculated?
In APR mode the daily rate is simply the nominal annual rate divided by the day-count basis: 5% ÷ 365 gives 0.013699% a day (shown as 0.0137%). In APY mode, available only for compounding, the calculator inverts the effective rate: dailyRate = (1+APY)^(1/365) − 1, so a 5% APY becomes 0.013368% a day and the basis is ignored because it already annualizes over 365 days. Simple accrual always reads the figure as a nominal APR, with no APY option.
Why does an actual/360 rate earn more than its nominal figure?
The basis is only the denominator that turns an annual rate into a daily one; it does not shorten the year. Actual/360 divides by 360, so each day's rate is a touch higher, yet interest still accrues over all 365 calendar days. At 6% APR compounding daily, actual/360 gives a 0.016667% daily rate, a 6.272% annualized yield, and $627.16 of interest on $10,000 — against the $600.00 a plain 6% implies. That extra $27.16 is the actual/360 kicker.
If I enter an APY, will the tool give me back that exact yield?
Yes. APY mode is built so a full 365-day compounding run reproduces the rate you typed. Enter 5% APY on $10,000 and the calculator derives a 0.013368% daily rate; compounded across 365 days the interest lands at exactly $500.00, ending at $10,500.00 — a clean 5% return. Because the daily rate is found by inverting (1+APY)^(1/365)−1, the day-count basis plays no part here. Change the horizon away from 365 days and the realized percentage will naturally differ.
How do recurring deposits earn interest?
Deposits can be added daily, weekly, biweekly or monthly, with monthly treated as a fixed 30-day interval. Each deposit posts at the end of its day and begins earning the next day, so money you add today does not earn on the day it arrives. Over a year that means 365 daily, 52 weekly, 26 biweekly or 12 monthly deposits. Adding $100 a week to $10,000 at 4% APR compounding contributes $5,200 in deposits, earns $511.73 of interest, and ends at $15,711.73.
How is tax applied?
Tax is charged on interest only, never on your own deposits or principal. The calculator sweeps it once a year and again on the final day, and the ending balance it reports is already after tax. Take $10,000 at 5% APR compounding over 730 days: gross interest is $1,045.85, tax at 22% removes $230.09, leaving $815.76 of after-tax interest and a $10,815.76 balance. Because tax is deducted along the way, it slightly reduces the base that later interest compounds on.
What does the inflation adjustment show?
Inflation does not change how interest accrues; it restates your after-tax ending balance in today's money, so you can see real buying power rather than a headline number. The tool deflates the final figure over the horizon measured as days ÷ 365 years. Continuing the $10,000, 5% APR, 730-day example with 22% tax and 3% inflation: the after-tax balance of $10,815.76 is worth $10,194.89 in today's money. The nominal gain stays the same — inflation simply tells you what it is actually worth.
Can the calculator work backwards from a goal?
It can. Alongside the forward projection sit four reverse modes. You can solve for the annual rate needed, the starting balance needed, the recurring deposit needed, or the number of days needed to reach a target ending balance. For instance, growing $10,000 into $11,000 in 365 days by daily compounding requires a 9.53% APR. Growing $10,000 to $10,500 at 5% APR compounding takes 357 days. Each mode holds your other inputs fixed and searches for the single figure that hits the target.
Will this match the interest my bank actually pays?
Treat it as a close estimate, not a promise. Three things make banks differ: day-count basis (some use actual/360, others actual/365), rounding (many round each day's interest to the cent, which the raw formula does not), and the gap between crediting and compounding — a bank may accrue daily but only pay, or begin compounding, monthly. Your bank may also apply tiered rates or fees this tool ignores. The numbers here show how daily interest behaves in principle; your statement can land a few cents either side.
How is this different from the Simple Interest, Compound Savings and Effective Interest Rate calculators?
Each runs a different clock or job. The Simple Interest calculator applies flat interest over a term counted in years, with no compounding. Compound Savings and Bank Interest tools compound on a monthly or annual schedule, not daily. The Effective Interest Rate tool converts one rate into another and stops there. This calculator runs a genuine day-by-day clock, can compound each day, and applies the rate to real money — deposits, tax and inflation included — rather than just quoting a converted figure.
What does the calculator not cover?
To keep the daily clock clean, several real-world details are left out. It does not model account fees, so a monthly maintenance charge won't appear. It ignores specific calendar dates, holidays and weekends — every day accrues. It assumes one fixed rate throughout, so variable or promotional teaser rates aren't handled. And in simple mode there is deliberately no compounding at all. For fees, changing rates or exact posting dates, check your account terms; this tool is built to isolate how daily interest itself works.
Does the daily interest amount stay the same each day?
It depends on the accrual style. Under simple interest the daily amount is constant, because interest is always figured on the unchanging principal — that is why 365 days at 5% on $10,000 gives an even $500.00. Under daily compounding the amount climbs: the first day earns $1.37, but as interest joins the balance later days earn a little more, averaging about $1.40 across the year to total $512.67. The rise is gentle over twelve months and becomes far more noticeable over multi-year horizons.
Can I use it for a short period, like a single month?
Short horizons are exactly where a daily clock earns its keep, since day-by-day accrual matters most over a handful of days. Set 30 days on $10,000 at 4.5% APR compounding and the tool returns $37.05 of interest for an ending balance of $10,037.05. Because it counts actual days rather than rounding to a whole month, it suits bridge periods, notice accounts or working out interest between two paydays. The horizon can run anywhere from a single day up to 3,650 days, or ten years.