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See how a traditional 401(k) deferral changes this paycheck’s take-home and estimated annual income-tax savings.
Last updated 3 October 2026
Estimates only — not tax, payroll, or financial advice. This is a simplified educational calculator (2026-ish federal brackets + standard deduction, employee FICA, optional flat state tax). It is not IRS Publication 15-T withholding, a substitute for your W-4, or a tax return. Real paystubs vary with credits, benefits, local taxes, additional Medicare tax, and your employer’s payroll system. Confirm numbers with a qualified tax or payroll professional.
$24,500. That is the most you may defer from your own pay into a 401(k) in 2026, and it is the single number this slider does not know. It works in percent; the law works in dollars. On a $65,000 salary the limit arrives at roughly 37.7% and the slider goes to 50, so the top third of its travel describes a contribution the plan would have to refuse.
What follows is the arithmetic of a deferral — what each dollar actually costs you this fortnight, which taxes it moves and which it does not — and then the four separate ceilings a percentage box cannot see.
Take $65,000 paid biweekly, single filer, no state tax. With nothing deferred the estimated deposit is $2,092.60. At 6% the deferral is $150.00 a paycheck and the deposit becomes $1,960.60. The paycheck is $132.00 smaller and the retirement account is $150.00 bigger, so each dollar saved costs 88 cents of spendable pay.
The missing 12 cents is not a discount, a match or a trick. It is the federal marginal rate on the income that stopped being taxable. Over the year, $3,900 is deferred and the estimated federal tax falls from $5,620 to $5,152, which is $468 — exactly 12% of $3,900, the bracket that $65,000 of income sits in. Push the slider to 10% and the pattern holds: $250.00 a paycheck deferred, a $220.00 smaller deposit, 88 cents per dollar again, and $780 of annual tax avoided on $6,500 deferred. The ratio only changes when the deferral drops you into a lower bracket, which on this salary it does not.
This is why the same percentage is worth more to a higher earner. The cost per dollar is one minus your marginal rate, so a filer in the 24% band keeps 76 cents of cost per dollar saved, and a filer whose taxable income is below $12,400 is in the 10% band and keeps 90 cents of cost. Read the figure the calculator gives you as a price, and compare it with what you would otherwise have done with the money.
Publication 15's table of special rules has one line for this, and it is worth reading across all three of its columns. The row is “Elective employee contributions and deferrals to a plan containing a qualified cash or deferred compensation arrangement (401(k))”. Under Federal income tax withholding it says “Generally exempt, but see section 402(g) for limitation”. Under Social security and Medicare (including Additional Medicare Tax when wages are paid in excess of $200,000) it says “Taxable”. Under FUTA it says “Taxable”.
So a traditional deferral reduces the wages your income tax is figured on and does nothing at all to FICA. You can watch that in the result panel: on $65,000 the annual Social Security and Medicare total is $4,972.50 at 0%, at 6%, at 10% and at 50%. It does not move, because it cannot. And the 6.2% is still being charged on wages you never saw, which also means those wages still count toward your Social Security earnings record.
The same row carries the pointer to the limit. Section 402(g) is the elective deferral cap, and that is the $24,500.
Federally an elective deferral comes out before income tax, and most states follow that. Pennsylvania does the opposite. Its employer withholding guide, REV-415, lists among things that are compensation: “Payments by employers into pension plans, 401(k) plans or other retirement plans made pursuant to the employee's election, by salary reduction agreement or through periodic payroll deductions, are taxable to employees and should be included in Pennsylvania gross wages on their W-2 forms.”
So the size of it, worked through at $65,000 biweekly with 6% deferred and Pennsylvania's flat 3.07%. Charging state tax on wages after the deferral means $61,100 of wages and $72.14 a paycheck. Pennsylvania charges it on the whole $65,000, which is $76.75 a paycheck, and over a year the difference is $119.73. Until 3 October 2026 this page only applied the first of those and told you to read the state saving as federal only. Now you pick your state above, and choosing Pennsylvania charges the full wage: the tax-saved figure on this page falls from $587.73 to $468.00, which is that same $119.73.
What the state box does and does not know. It carries a row per state whose treatment has been read from that state's own revenue department, and nothing else. Today that is Pennsylvania and New Jersey. Every other state uses a default that applies the federal treatment, and the note under the box says so, because that default is an assumption and not a finding: there is no fifty-state survey behind this page. If you know your state taxes 401(k) contributions and it is not listed, the figure here is light by your rate times your deferral, the same way Pennsylvania's was.
New Jersey is in the list to mark a trap rather than a difference, because for a 401(k) it agrees with federal law. Its Division of Taxation says it “does not allow you to exclude from wages amounts you contribute to deferred compensation and retirement plans, other than 401(k) Plans”, naming 403(b), 457, 409A, 414(h), SEP and IRA contributions as ones you cannot exclude. This page models a 401(k) and only a 401(k), so a New Jersey reader putting 403(b) contributions into the box gets the Pennsylvania problem without the warning.
Two things the state box deliberately does not do. It does not supply a rate for any state except Pennsylvania, whose 3.07% is flat and published, because most states run graduated brackets that a single percentage cannot represent and inventing one would read as precision. And it changes only the 401(k) treatment, not the rest: there are still no state standard deductions, no local or city income tax, and no credits anywhere in these figures.
The IRS Roth comparison chart draws the distinction in one line: designated Roth employee elective contributions “are made with after-tax dollars”, whereas traditional, pre-tax employee elective contributions “are made with before-tax dollars”. A Roth deferral therefore reduces your deposit by the full amount and saves you nothing today, so every tax-saved figure on this page would be zero. The same chart confirms that pre-tax deferrals carry the “Same aggregate limit as designated Roth 401(k) account” — one $24,500 ceiling covers both, however you split them. (That chart's own dollar figures were last stated for 2024, which is why the 2026 limit above is quoted from the contribution-limits page instead.)
The slider stops at 50% and the number box beside it accepts up to 100, both beyond anything a plan would run, so the page caps what it will actually apply. On $65,000 biweekly a 50% election asks for $32,500 a year, which is $8,000 over the limit, so the page applies $24,500, or $942.31 a paycheck, and the take-home reads $1,263.37. At 100% it applies the same $24,500, because the limit binds first.
Until 3 October 2026 it applied whatever you typed. A 50% election deferred $32,500, over the limit, and 100% produced a take-home of −$191.25. That was never a bug in the subtraction: at a full deferral there is no cash left to pay the $155.00 of Social Security and $36.25 of Medicare still owed on the full wage. The arithmetic was honest and no payroll system would produce it, because a plan refuses the election instead, and now so does this page.
A second cap catches what the limit cannot. On a salary low enough that all of it sits under $24,500, deferring everything still leaves FICA unpaid: $20,000 at 100% applies $18,470 and brings the take-home to exactly $0.00, which is as far as the arithmetic goes. Neither cap applies a catch-up amount — $8,000 at 50 and over, $11,250 for ages 60 to 63 — because this page does not ask your age and will not guess it.
Part of the PaystubKit tools collection. Calculations run locally in your browser. Estimates only, not tax or investment advice.
On $65,000 paid biweekly as a single filer, $150.00 goes into the 401(k) and the estimated deposit falls from $2,092.60 to $1,960.60 — a drop of $132.00. So a dollar saved costs 88 cents of spendable pay. The 12-cent gap is the 12% federal bracket that income sat in.
No. Publication 15's special-rules table marks elective 401(k) deferrals “generally exempt” from federal income tax withholding and “taxable” for Social Security and Medicare. On $65,000 the annual FICA total stays at $4,972.50 whether you defer 0%, 6%, 10% or 50%.
Yes, since 3 October 2026. The 2026 elective deferral limit is $24,500 and the slider is now held to it: on $65,000 the slider's 50% setting asks for $32,500 and the page applies $24,500. The catch-up amounts ($8,000 at 50 and over, $11,250 at ages 60 to 63) are deliberately not applied, because this page never asks your age and applying one would be guessing on your behalf. Before that date no dollar cap was applied at all and the 50% setting really did describe $32,500.
No, and this is the most common mix-up. The match counts against the separate limit on total annual additions, which for 2026 is the lesser of 100% of your pay or $72,000 ($80,000 including catch-up, or $83,250 at ages 60 to 63). The match is not modelled on this page at all.
Yes, if you pick Pennsylvania in the state box. Pennsylvania treats elective 401(k) deferrals as taxable compensation, so it withholds on the full wage. At $65,000 with 6% deferred and 3.07%, charging state tax on wages after the deferral gives $72.14 a paycheck, while Pennsylvania's own rule gives $76.75, a difference of $119.73 a year. Choosing Pennsylvania applies the second one, and the tax-saved figure on this page falls from $587.73 to $468.00. Leaving the box on the default applies the federal treatment, which is what most states do but has not been checked state by state.
No. Estimates only — not tax, payroll, or financial advice. There is no investment return, fee or future tax rate in these figures, and nothing here checks your plan document.