401(k) Paycheck Impact Calculator
Two percentages, and the difference between them
Your result will appear here
Fill in the fields on the left and this updates as you type.
Know what this estimate is based on
- Jurisdiction
- General mathematical model
- Scope and limitations
- Planning indicator only. It does not assess every part of a household's finances or replace individualized professional advice.
- 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 your annual salary — both scenarios are computed from it, so it is the only pay figure the page needs.
- 02
Enter the percentage you defer now, then the percentage you are thinking of moving to. The headline is the difference between the two: a single-scenario take-home figure is what the paycheck calculator already reports, and it is not the question anyone asks at open enrollment.
- 03
Enter the employer match as two numbers — the rate (50 means fifty cents on the dollar) and the share of pay it applies to. Fifty per cent on the first 6% is the commonest formula in the country.
- 04
Add your top federal bracket, your state rate, the years until you would draw on the money and the return you assume. The bracket is what the deferral comes off the top of, so it sets the whole tax saving.
- 05
Check the pay periods a year and the $24,500 deferral limit, then read the drop per paycheck against the cost of every dollar saved — and check the match line, because the difference between the two percentages may be partly paid by someone else.
Formula
Deferral at a percentage = salary × percentage, capped at the $24,500 elective limit. Employer match = min(your percentage, the match ceiling percentage) × the compensation the plan may count (salary, capped at $360,000) × the match rate. FICA = 6.2% on salary up to the $184,500 wage base + 1.45% on all of it, and it is IDENTICAL in both scenarios by construction — a deferral never reduces it. Take-home at a percentage = salary − deferral − (salary − deferral) × (marginal federal rate + state rate) − FICA. The headline is the difference between take-home at the two percentages, divided by pay periods a year. Cost per dollar saved = the drop in take-home ÷ the extra deferral. Income tax saved = the extra deferral × (marginal + state rate). Where the state does not exclude the deferral — Pennsylvania — the state line is charged on the FULL salary instead of on salary less the deferral, so the drop is larger by the deferral × the state rate. Projected balance grows each year as balance × (1 + return) + deferral + match, run for both percentages and differenced.
Example
An $82,000 salary, moving from 5% to 10%, with a 50% match on the first 6%, a 22% federal bracket, no state income tax, biweekly pay, 30 years at 7%. The deferral goes from $4,100 to $8,200 — an extra $4,100 a year, $158 a paycheck. Taxable pay falls from $77,900 to $73,800, so income tax falls by $902. Social Security and Medicare stay at $6,273 in both scenarios, unchanged by a cent. Take-home falls from $54,489 to $51,291: a drop of $3,198 a year, $123 a paycheck, which is 78 cents for every dollar saved. The match moves too — $2,050 captured at 5%, the full $2,460 at 6% and above, so the $410 you were forfeiting comes back. Total into the account goes from $6,150 to $10,660 a year. Over 30 years at 7% that is $1,006,951 against $580,933, a gap of $426,018 bought with $95,940 of forgone take-home. The ladder on the same salary: 0% leaves $2,219 a paycheck, 6% leaves $2,071 and captures the whole match, 10% leaves $1,973, and 15% leaves $1,850 — with the cost per dollar saved sitting at $0.78 all the way up, because the bracket does not change.
Definitions
- Elective deferral
- The money you choose to send into a 401(k) from your own pay, pre-tax or Roth. Capped at $24,500 for 2026 across every employer, before any age-based catch-up.
- Annual additions limit
- $72,000 for 2026 — everything credited to the account for the year, your deferrals plus employer money plus after-tax contributions. A separate and much higher ceiling than the elective limit.
- True-up
- A plan provision that pays any match you missed by hitting the deferral limit early. Common but far from universal; its absence is why front-loading can cost you money.
- Compensation limit
- $360,000 for 2026 — the most pay a qualified plan may count for any purpose, including the match. It caps the match however high the salary goes.
- Section 3121(v)(1)(A)
- The provision that includes elective deferrals in wages for Social Security and Medicare. It is the reason take-home falls by less than you defer, and the reason it does not fall by even less.
Good to know
Why the paycheck falls by less than you save
This is the fact that makes the whole decision easier than it looks, and it is not widely enough known. A pre-tax elective deferral comes off the top of your taxable income, so the income tax it saves is your marginal rate applied to the whole slice. Move from 5% to 10% on an $82,000 salary and $4,100 more goes into the plan — $158 a paycheck — but taxable pay falls from $77,900 to $73,800, so federal income tax falls by $902. Take-home therefore drops by $3,198 a year rather than $4,100: $123 a paycheck. Put another way, every dollar you put away costs you 78 cents of spendable pay, and the other 22 cents is tax you were going to hand over regardless. At a 24% bracket in a state with a 5% income tax the cost per dollar falls to about 71 cents; in the nine states with no wage income tax and a 12% bracket it is about 88 cents. The number is always below a dollar and the gap is always exactly your combined income-tax rate on the increment. That framing is worth carrying into an open-enrolment decision, because it reverses the usual mental accounting. The question is not 'can I afford to give up $4,100 of pay' — you are not giving up $4,100, you are giving up $3,198, and the $902 difference is not a reward for saving, it is simply tax deferred to a later year at whatever rate applies then. Whether that later rate is higher or lower than 22% is the genuine open question, and it belongs to the Roth-versus-traditional decision rather than to this page.
FICA is the line that never moves
The tax break has a hard boundary and it is worth knowing exactly where it sits. Elective deferrals are excluded from federal income tax under section 402(g), and expressly INCLUDED in wages for Social Security and Medicare under section 3121(v)(1)(A). Those two provisions are doing opposite things on purpose. So the payroll tax on an $82,000 salary — 6.2% of $82,000 up to the $184,500 wage base, plus 1.45% of all of it, $6,273 in total — comes out identically at 0%, at 5%, at 10% and at 15% of pay. There is no contribution percentage anywhere on the scale that reduces it by a single cent. This is why take-home falls by less than you defer but by more than the income tax saving alone would suggest, and it is the reason the cost per dollar saved sits at $0.78 rather than at $0.70. It has an upside that rarely gets mentioned. Because Social Security tax is paid on the money when it is earned, your deferral has already bought the Social Security credit for the year; the benefit formula sees your full $82,000, not the $73,800 you were taxed on. And the money is never charged FICA again — not when it grows, and not when it comes out in retirement. The pattern is different for a Roth deferral, where income tax is paid up front too, so the paycheck drop and the contribution are the same number: moving $4,100 into a Roth 401(k) costs the full $4,100. It is different again for a section 125 health premium, which escapes income tax AND payroll tax, and is therefore the cheapest dollar of the three to defer.
The match is the part someone else pays
For anyone below the match ceiling, the employer formula changes the answer far more than the tax break does. A 50% match on the first 6% of an $82,000 salary is worth $2,460 a year in full. At 5% you capture $2,050 and forfeit $410; at 6% and above you capture all of it, because the match stops at 6% however much more you defer. That forfeited $410 is not an opportunity cost or a projection — it is compensation you were offered and declined, and it is the only line anywhere on this page with an instant and certain fifty per cent return. The first number worth reaching in any plan is whatever captures the whole match, and only then does the question of going further become a genuine investment decision. Three details around the match are worth checking in the summary plan description rather than assuming. VESTING: match dollars may be subject to a cliff or a graded schedule, so leaving at month twenty can forfeit money the statements have been showing you for two years, while your own deferrals are always immediately yours. TRUE-UP: the match is usually computed per pay period, so if you hit the $24,500 elective limit in September, the deferral stops and at a plan without a true-up provision the match stops with it — on an $82,000 salary you reach the limit at about 29.9% of pay, so anyone deferring at that level should check before front-loading. And the COMPENSATION LIMIT: a qualified plan may only count $360,000 of pay for 2026, so the match is capped at the formula applied to that figure however high the salary goes. Over 30 years at 7%, the 5%-to-10% move on these numbers puts $426,018 more in the account, and $12,300 of the contributions behind it is employer money.
Where your state, and the shape of your election, change the answer
The main figures on the page assume your state follows the federal treatment and excludes an elective deferral from taxable wages. Most do. Pennsylvania does not: it taxes elective deferrals as compensation at the moment they are made, and exempts the qualifying distribution later instead. The page therefore computes both treatments on every render rather than asking you to pick a state, but the difference only becomes visible once you enter a state rate — at a zero state rate the two answers are identical by construction, so a blank state field will show no penalty at all. Enter Pennsylvania's 3.07% and the same $4,100 move costs roughly $126 a year more than the standard treatment, because the state charges its rate on the full salary rather than on salary less the deferral. Nine states levy no tax on wage income at all, where the state line is zero either way and only the federal saving is real. Two practical points close the subject. First, set the election as a PERCENTAGE rather than a dollar amount wherever the plan offers both: a percentage tracks your pay and rises with every raise on its own, while a flat dollar amount silently decays as a share of income until you happen to notice. Second, remember that a pre-tax balance is a pre-tax number. The $1,006,951 projected at 10% is not comparable with a Roth balance of the same size, because ordinary income tax is due on every dollar of it as it comes out. Comparing a traditional and a Roth projection without adjusting for that overstates the traditional account by whatever your retirement rate turns out to be.
Frequently asked questions
How much will my paycheck actually drop if I contribute more?
By less than you put away, always. Moving from 5% to 10% on an $82,000 salary sends an extra $4,100 a year into the plan — $158 a paycheck — but take-home falls by only $3,198 a year, or $123 a paycheck. The gap is $902 of federal income tax the deferral no longer pays. Every dollar you defer costs you 78 cents of spendable pay and the other 22 cents is tax you were going to pay anyway.
Why doesn't the deferral reduce Social Security and Medicare too?
Because the statute treats them differently on purpose. Elective deferrals are excluded from income tax under section 402(g) but expressly INCLUDED in wages for FICA under section 3121(v)(1)(A) — the money is taxed for Social Security and Medicare when it is earned, and never again when it comes out. So the $6,273 of payroll tax on an $82,000 salary is identical at 5% and at 10%, and there is no percentage you can pick that reduces it by a cent. The compensation is that the deferral has already bought your Social Security credit for the year.
What does the employer match do to the arithmetic?
It changes the answer more than the tax break does, if you are below the match ceiling. On a 50% match on the first 6% of an $82,000 salary the full match is $2,460. At 5% you capture $2,050 and forfeit $410; at 10% you capture all $2,460, because the match stops at 6% however much more you defer. That $410 is not a projection or an opportunity cost — it is compensation you were offered and declined, and it is the only line on the page with an instant, certain return.
Does a Roth 401(k) work the same way?
No — with a Roth deferral none of the tax saving exists. Roth money is contributed from taxed pay, so the paycheck drop and the contribution are the same number: moving $4,100 into a Roth 401(k) costs the full $4,100 of take-home rather than $3,198. The match is unaffected either way and still lands in a pre-tax account. Whether the extra $902 a year of present cost buys enough tax-free growth to be worth it is a real question with a real answer, and it turns on whether your rate in retirement is above or below your rate today.
My state taxes my 401(k) contributions — does that change anything?
It does, and Pennsylvania is the case. Most states follow the federal treatment and exclude an elective deferral from taxable wages, which is what the main figures assume. Pennsylvania does not: it taxes elective deferrals as compensation when they are made and exempts the distribution later instead. The page computes both treatments, but the difference only becomes visible once you enter a state rate — at a zero state rate the two answers are identical by construction. At a 3.07% Pennsylvania rate the same $4,100 move would cost about $126 a year more.
Can I contribute too much, too fast?
You can hit the $24,500 elective limit before December, and at some employers that costs you match dollars. The match is usually computed per pay period, so once your deferral stops the match stops with it — and a plan with no true-up provision simply does not pay the months you sat at the ceiling. On an $82,000 salary you reach the limit at about 29.9% of pay, so anyone deferring at that level or above should check the summary plan description for the words 'true-up' before front-loading.
Should I set the plan in dollars or in percentages?
Percentages, wherever the plan offers both. A percentage tracks your pay: every raise raises the deferral on its own, with no action from you. A flat dollar amount silently falls as a share of income year after year until you happen to notice. It is the difference between a decision that keeps working while you are not looking and one that decays.
What is the change actually worth in the end?
On these numbers, $426,018 more in the account after 30 years at a 7% return — $1,006,951 against $580,933 — against $95,940 of forgone take-home over the same period. Of the extra balance, $12,300 is employer match money in undiscounted dollars, which is the part that costs you nothing at all. Remember that a pre-tax balance is a pre-tax number: it is taxed as ordinary income on the way out, so it is not directly comparable with a Roth balance of the same size.