Mortgage Amortization Calculator
Loans & MortgagesPrincipal vs interest, month by month.
Loan details
Enter a loan amount above zero to see your amortization schedule.
Advanced — extra payments
Enter a loan amount above zero to see your amortization schedule.
Know what this estimate is based on
- Jurisdiction
- General model; U.S.-specific rules are identified on the relevant tool
- Scope and limitations
- Educational estimate only. A lender may use different compounding, day-count, eligibility, tax, insurance, escrow, fee, or rounding rules.
- 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
Enter the loan amount, the annual interest rate and the term in years. The calculator instantly returns your fixed monthly principal-and-interest payment and the total interest over the life of the loan.
- 02
Open Advanced to add a recurring extra monthly payment and/or a one-time lump sum, and choose which month the lump lands on — the schedule re-runs to show the interest saved and the years shaved off.
- 03
Scroll the principal-vs-interest chart, the year-by-year summary and the full month-by-month amortization table, then Save & compare scenarios or Share the link to revisit the numbers later.
Formula
Amortization is the process of paying off a loan with equal periodic payments. Each payment is split between interest (charged on the balance still owed) and principal (what's left, which reduces the balance). Early on almost all of it is interest; near the end almost all of it is principal. Step 1 — The monthly payment. With principal P, a monthly rate i (annual rate ÷ 12) and n monthly payments, the level payment is M = P · i · (1 + i)ⁿ ÷ ((1 + i)ⁿ − 1). For a $300,000 loan at 6.5% over 30 years, i = 0.5417% and n = 360, which gives M = $1,896.20 a month. Step 2 — Splitting each payment. Month one charges interest of $300,000 × 0.5417% = $1,625, so only $1,896.20 − $1,625 = $271.20 goes to principal. As the balance falls the interest portion shrinks and the principal portion grows, which is why the split flips over the life of the loan. In year one you pay about $19,401 in interest but only $3,353 of principal. Step 3 — Total interest and total cost. Over all 360 payments you pay M × n = $1,896.20 × 360 = $682,633. Subtract the $300,000 borrowed and the interest alone is $382,633 — about 1.27 times the amount borrowed, or 56% of every dollar you hand over. That is the real headline of a long mortgage. Step 4 — Extra payments. Any amount paid above the scheduled payment goes straight to principal, so it never accrues interest again — and the savings compound. Adding $200 a month clears this loan in 23 years 1 month instead of 30 years, saving $103,449 in interest and 6 years 11 months. A single $20,000 lump in month 12 saves $91,623 and 4 years 10 months. You still only ever repay the $300,000 you borrowed; extra payments simply buy back future interest. Step 5 — Payoff date. Counting the months to a zero balance from your start date gives the payoff date. With extra payments the loan reaches zero earlier — the gap between the two is the time you save.
Example
Priya borrows $300,000 to buy a home, on a 30-year fixed mortgage at 6.5%. The calculator returns a monthly principal-and-interest payment of $1,896.20. At first the split is sobering. Her very first payment is $1,896.20, but $1,625 of it is pure interest on the $300,000 balance — only $271.20 actually pays down the loan. Across the whole first year she pays about $22,754, of which roughly $19,401 is interest and just $3,353 is principal. Stretched over 360 payments, she will hand the lender $682,633 in total: the $300,000 she borrowed plus $382,633 in interest. Interest is the single biggest line item — 1.27 times the loan itself. Then Priya tests an extra $200 a month. Because every extra dollar goes straight to principal, the balance falls faster and less interest can accrue on it. Her payoff drops from 30 years to 23 years 1 month, and her lifetime interest falls from $382,633 to $279,185 — a saving of $103,449 and very nearly seven years, for $200 a month she barely notices. Curious about a windfall, she instead models a one-off $20,000 payment in month 12 — say from a bonus. That single lump, applied early while the balance is high, saves her $91,623 in interest and shortens the loan by 4 years 10 months. The lesson the amortization schedule makes vivid: on a long loan, interest dwarfs principal, and the earlier you attack the balance the more you save.
Definitions
- Amortization
- Repaying a loan through equal periodic payments, each split between interest on the outstanding balance and principal that reduces it. The mix shifts from mostly interest to mostly principal over the term.
- Principal
- The amount you actually borrowed. Each payment chips a little off it; extra payments reduce it directly. You only ever repay the principal once — the rest of what you pay is interest.
- Interest
- The lender's charge for the money, calculated each month on the balance still owed. Because the balance is highest at the start, early payments are mostly interest.
- Monthly payment (P&I)
- The fixed principal-and-interest payment that fully repays the loan over the term: M = P · i · (1+i)ⁿ ÷ ((1+i)ⁿ − 1). It does not include property tax, insurance or HOA dues.
- Amortization schedule
- The month-by-month table showing, for each payment, how much went to interest, how much to principal, and the balance remaining afterward.
- Total interest
- The sum of the interest portion of every payment — payment × number of payments, minus the amount borrowed. On long loans it often exceeds the principal itself.
- Extra payment
- Any amount paid above the scheduled payment. It applies entirely to principal, so it removes future interest on that amount and shortens the loan — recurring monthly, as a one-time lump, or both.
- Interest saved
- The difference between the total interest on the standard schedule and the total interest once extra payments are applied. It is money you keep, not money you pay.
- Payoff date
- When the balance reaches zero. Extra payments move it earlier; the months between the standard payoff and the accelerated payoff are your time saved.
Good to know
What it means to amortize a loan
To amortize a loan is to pay it off gradually through a series of equal payments, each one part interest and part principal. The word descends from the Latin for "to bring to death" — every payment kills off a little more of the debt until, on the final month, the balance lands exactly on zero. A fixed-rate mortgage is the textbook example: you agree a single monthly payment at the start, and that number never changes, yet what it is doing under the hood changes completely from the first month to the last. That hidden shift is the part most borrowers never see, and it is exactly what this calculator lays bare. The reason the payment can stay level while its job transforms is that interest is always charged on the balance you still owe. At the beginning that balance is at its largest, so the interest slice of each payment is fat and the principal slice is thin. Every payment you make shrinks the balance a little, so next month's interest is slightly smaller and slightly more of the same fixed payment is free to attack the principal. Repeat that 360 times on a 30-year loan and the composition of the payment flips entirely — from almost all interest to almost all principal — even though the dollar amount you write the cheque for never moves. It is worth saying what amortization is not: if a payment is ever smaller than the interest due, the shortfall is added back to the balance and the debt grows instead of shrinks — so-called negative amortization, seen in some interest-only or option-ARM loans. This calculator models the healthy case: a fully-amortizing, fixed-rate loan that is guaranteed to reach zero on schedule. Understanding this single mechanic explains everything else that follows — why a long loan costs so much in interest, why early extra payments are so powerful, and why two loans with the same monthly payment can cost wildly different amounts over their lives. The amortization schedule is simply the month-by-month record of the process, and learning to read it is the fastest way to understand what your mortgage is really doing with your money.
What sets your monthly payment
Three numbers determine your fixed monthly principal-and-interest payment: the amount you borrow, the interest rate and the length of the loan. The formula that ties them together is M = P · i · (1 + i)ⁿ ÷ ((1 + i)ⁿ − 1), where P is the principal, i is the monthly interest rate (the annual rate divided by twelve) and n is the total number of monthly payments. It looks forbidding, but its behaviour is intuitive. Borrow more and the payment rises in direct proportion — double the loan and you double the payment. Raise the rate and the payment climbs too, but not in a straight line: because interest compounds on the balance every month, each additional percentage point costs more than the one before it. Stretch the term and the payment falls, since the same principal is spread over more months — but, crucially, a lower payment from a longer term does not mean a cheaper loan, because every one of those extra months carries its own interest. On the default $300,000 loan at 6.5% over 30 years, the formula returns $1,896.20 a month. Hold the loan and rate fixed but shorten the term to 15 years and the monthly payment rises by several hundred dollars, yet the total interest collapses, because the balance is cleared in half the time and interest has far fewer months to accrue. Move the rate instead — even by half a percentage point — and you will see the payment and the lifetime cost both shift by a surprising amount, which is why shopping lenders and improving your credit profile before you borrow is worth real effort. This is the central trade-off of choosing a mortgage: a longer term buys a smaller, more affordable monthly payment at the price of far more interest overall, while a shorter term or lower rate demands more discipline up front but costs dramatically less in total. The calculator lets you move each of the three levers independently and watch both the payment and the lifetime cost respond in real time, so the trade-off stops being abstract and becomes a pair of numbers you can weigh directly against your budget.
Why your early payments are almost all interest
The most counter-intuitive feature of an amortizing loan is how little of your early money actually reduces the debt. Take the very first payment on the default loan. The balance is the full $300,000, so one month's interest at 6.5% is $300,000 × (0.065 ÷ 12) = $1,625. Your payment is $1,896.20, so after the interest is taken only $271.20 is left to reduce the principal. In other words, in month one, about 86 cents of every payment dollar is rent on the money and just 14 cents buys down the loan. Zoom out to the first full year and the picture is the same: of roughly $22,754 in payments, around $19,401 is interest and only $3,353 touches the principal. This front-loading is not a fee or a trick — it falls straight out of charging interest on a large early balance — but it has real consequences. It is why your balance barely seems to move in the first few years; why being "five years into a thirty-year loan" leaves you nowhere near a fifth of the way paid off; and why selling or refinancing early means you have built almost no equity through payments alone, having instead spent those years mostly covering interest. It also explains the lender's economics: the institution is largely paid for its risk in the opening years, which is part of why some loans historically carried prepayment penalties (worth checking your own loan documents for). As the years pass the balance finally falls far enough that the arithmetic tips. Somewhere past the midpoint of the loan, the principal portion of each payment overtakes the interest portion, and from that crossover onward the balance drops faster and faster, snowballing toward zero. The calculator's month-by-month table shows this turning point explicitly, row by row, and the principal-versus-interest chart makes the shifting mix visible at a glance — the single clearest picture of where each payment dollar is really going across the life of the loan.
The real cost of a long mortgage
A monthly payment is only half the story; the other half is what the loan costs in total, and on a long mortgage that number is startling. Multiply the default payment by the number of payments — $1,896.20 × 360 — and you get $682,633. Subtract the $300,000 you borrowed and the interest alone comes to $382,633. You pay roughly 1.27 dollars of interest for every dollar borrowed, and 56% of every dollar that leaves your account over thirty years is interest rather than principal. That is the true price of spreading a loan across three decades, and it is invisible if you look only at the comfortable monthly figure. Two forces drive the total, and both reward attention before you sign. The first is the rate: because it compounds on the outstanding balance every single month, even a fraction of a percentage point, multiplied across hundreds of payments, can swing the lifetime interest by tens of thousands of dollars. That is why a slightly lower rate, or paying discount points up front when you will hold the loan a long time, can be worth far more than it appears — and why the APR, which folds fees into the rate, is the fairer way to compare offers. The second force is the term. A 30-year loan keeps a large balance outstanding for a long time, and interest feeds on that balance for all 360 months; halving the term to 15 years roughly halves the months over which interest can accrue and slashes the total, even though the monthly payment is higher. Seeing total interest and total cost side by side with the monthly payment — as this calculator deliberately puts them — reframes the whole decision. The cheapest-looking payment is frequently attached to the most expensive loan, and the sharper question is not only "can I afford the monthly payment?" but "how much am I willing to pay in total for the privilege of borrowing this money?" The answer often nudges borrowers toward a shorter term, a larger down payment, or a harder push on the rate.
How extra payments rewrite the schedule
The most powerful lever an ordinary borrower controls is the extra payment, and the amortization schedule explains exactly why it works so well. A scheduled payment is split between interest and principal, but any amount you pay above it has no interest to cover — it applies entirely to principal. That dollar of principal is then gone for good, and so is all the future interest it would otherwise have generated, month after month, until the loan ended. The savings therefore compound, and they are largest early in the loan when the balance — and the interest riding on it — are at their peak. The numbers are persuasive. On the default loan, adding just $200 a month, money many households spend without noticing, clears the mortgage in 23 years and 1 month instead of 30 years, cutting the lifetime interest from $382,633 to $279,185. That is $103,449 saved and very nearly seven years of payments avoided, in exchange for a modestly larger cheque each month. A one-time lump sum behaves the same way but in a single stroke: a $20,000 payment made in the first year — a tax refund, a bonus, a small inheritance — saves $91,623 in interest and shortens the loan by 4 years and 10 months, precisely because it lands while the balance is high and erases interest that would have compounded for decades. The same $20,000 paid in year twenty would save a small fraction of that, which is the whole point about timing: early dollars are worth far more than late ones. It is worth distinguishing prepaying from recasting. Prepaying, which this tool models, keeps your payment the same and shortens the loan. Recasting (re-amortizing) instead keeps the term and lowers the payment after a lump sum — useful for cash flow, but it saves less interest than letting the term shrink. Paying half your payment every two weeks is simply prepaying in disguise: twenty-six half-payments equal thirteen monthly payments a year, one extra, which you can model here as roughly a month's payment spread across the year. Crucially, extra payments never increase what you ultimately repay in principal — you still owe only the amount you borrowed; they merely buy back future interest at a steep discount. The calculator lets you model a recurring extra, a one-time lump, or both together, and reports the interest saved and the time shaved against the untouched schedule, so you can compare strategies before committing a single dollar.
Reading the schedule, the yearly summary and your payoff date
An amortization schedule can run to 360 rows, so this calculator gives you three lenses on the same data, from the big picture down to the individual payment. The headline results answer the questions most borrowers actually have: what is my monthly payment, how much interest will I pay in total, and what will the whole loan cost? Beneath that, the year-by-year summary condenses the loan into one row per year — how much principal and interest you paid that year, any extra applied, and the balance still owing at year-end. This is the right altitude for spotting milestones: the year your balance finally dips below half the original loan, or the year the principal portion of your payments overtakes the interest portion. Then the full month-by-month table shows every payment in detail — the interest charged, the scheduled principal repaid, any extra applied, and the running balance afterward — so you can audit a specific payment or pinpoint exactly when the crossover happens. The payoff date pulls these together into a single, human answer: counting forward from today to the month the balance reaches zero. With the standard schedule that date is simply the end of the term; as soon as you add extra payments it jumps earlier, and the distance it moves is the time you have bought back. One small technical note worth understanding: because the payoff date depends on the current calendar, the calculator computes the exact duration to payoff immediately (it is pure arithmetic) and then fills in the actual calendar date once the page has loaded in your browser, so a cached or shared page never shows a stale date. Read together, these four views — headline, yearly, monthly and payoff date — turn an intimidating wall of numbers into a story you can follow from the first payment to the last.
What the payment leaves out, and how to use this well
This calculator models the loan itself — principal and interest, the part that genuinely amortizes — and nothing else. A real housing payment usually bundles in several costs that do not pay the loan down at all: property taxes, homeowner's insurance, private mortgage insurance if your down payment was under 20%, and any homeowners-association dues. Lenders collect these alongside the loan, and the combination is often abbreviated PITI (principal, interest, taxes and insurance), so the figure your lender quotes will be higher than the principal-and-interest payment shown here. Keeping the two separate is useful precisely because it isolates the amortizing core, but remember to add the rest back when you test the payment against your real budget — and note that some of those extras, such as private mortgage insurance, fall away over time as your equity grows, while taxes and insurance tend to drift upward. With that caveat in mind, the tool earns its keep across several decisions. Before you borrow, compare terms and rates to see how each reshapes both the monthly payment and the lifetime interest, and let that guide how much loan you are genuinely comfortable taking on. After you borrow, test extra-payment strategies — a steady monthly top-up, a windfall lump sum, or both — and use the saved-scenario comparison to find the plan that removes the most interest for the least strain on your cash flow. If you are weighing whether to refinance, amortize the prospective new loan here and set its lower rate or shorter term against your current schedule; the interest you would save has to clear the closing costs of the new loan before refinancing truly pays. And if a lender pitches an accelerated structure such as biweekly payments, model the equivalent extra against the standard monthly schedule to confirm the benefit is real and not merely a fee-bearing repackaging of something you could do yourself for free. Used this way, the amortization schedule stops being a document the lender hands you at closing and becomes a planning tool you control — one that turns the abstract weight of a mortgage into concrete, comparable numbers you can act on.
Frequently asked questions
Why is so much of my early payment interest instead of principal?
Interest is charged on the balance you still owe, and at the start that balance is at its highest. On the default $300,000 loan at 6.5%, the first month's interest is $1,625 of the $1,896.20 payment, leaving just $271.20 for principal. As the balance falls the interest charge shrinks and more of each fixed payment attacks the principal, so the split gradually flips — by the final years almost the entire payment is principal. The amortization table makes this crossover visible row by row.
How much interest will I really pay over the loan?
More than you might expect. On the default loan you repay $682,633 in total — the $300,000 borrowed plus $382,633 in interest, which is about 1.27 times the loan and 56% of every dollar you pay. The longer the term and the higher the rate, the larger that multiple grows, because interest accrues on the balance for more months. The total-interest and total-cost figures at the top of the results put the real price of the loan in plain sight.
How much do extra payments actually save?
A lot, because every extra dollar goes straight to principal and never accrues interest again. On the default loan, an extra $200 a month clears it in 23 years 1 month instead of 30 years, saving $103,449 in interest and nearly seven years. A one-time $20,000 payment in month 12 saves $91,623 and 4 years 10 months. Open Advanced to enter a recurring extra, a one-time lump, or both, and the results show the interest saved and time shaved versus the standard schedule.
Is it better to pay extra every month or make one big lump sum?
Both help; timing is what matters. A lump sum has its biggest effect when it lands early, while the balance — and therefore the interest it would have generated — is largest. A steady monthly extra is easier to budget and compounds its savings over many years. The calculator lets you model each separately or together, so you can compare a $20,000 windfall today against, say, $200 a month and see which removes more interest for your situation.
Does this payment include taxes and insurance?
No. This calculator shows principal and interest only — the part that actually amortizes the loan. Your full housing payment (often called PITI) also includes property tax, homeowner's insurance, any mortgage insurance and HOA dues, which are collected alongside the loan but don't pay it down. Keep that in mind when you compare this figure to a lender's quoted monthly payment, and use a full mortgage or affordability calculator for the all-in number.
What is the difference between the loan term and the payoff date?
The term is the scheduled length of the loan — 30 years here — which sets the monthly payment. The payoff date is when the balance actually reaches zero, which can be earlier if you pay extra. With the standard schedule the two coincide; add $200 a month and the payoff date jumps forward by 6 years 11 months. The calculator counts the months to a zero balance from your start date so you can see exactly when you'd be free of the loan.