Pre-Tax vs Post-Tax Deduction Calculator
See what a 401(k), an HSA, or a Section 125 premium each do to your taxable wages, FICA, and take-home pay, next to a Roth deferral or a garnishment.
Pre-Tax vs Post-Tax Deduction Calculator
Pay frequency
Used to project the annual figures. Every amount below is per paycheck, not per year.
Pay and deductions
What you earned this period, before anything comes out.
Cafeteria-plan dollars: exempt from income tax and from Social Security and Medicare. An HSA funded through payroll belongs here. An HSA you fund directly from your bank account does not (it is income-tax deductible, but FICA was already paid on it).
Exempt from income tax only. You still pay 7.65% FICA on every dollar you defer.
Comes out after taxes. Reduces take-home, reduces no tax at all.
Your tax picture
Your marginal rate, not your effective one. For 2026 the 22% federal bracket starts at $50,400 of taxable income for a single filer. Add your state rate on top if you have one.
Optional. Drives the $184,500 wage-base cap and the $200,000 Additional Medicare threshold. Read it off Box 3 of your last stub, or work it out with the YTD earnings calculator.
Deductions exceed gross pay for this period, so take-home comes out negative. Taxable wages are floored at zero, but a real payroll cannot withhold more than it pays.
A post-tax dollar always costs a full $1.00 of take-home. These are what the same dollar costs you once the tax it dodges is netted out, at your rate and your YTD position.
Same dollars, four ways
Every row moves the identical total deduction ($450.00 per period) into a different bucket. Only the bucket changes, and the take-home column moves anyway.
| Scenario | Section 125 | 401(k) | Post-tax | Total tax | Take-home |
|---|
Estimates only. Actual withholding depends on your Form W-4, state and local rules, and your employer's plan design. This is not tax advice.
How pre-tax and post-tax deductions change a paycheck
A pay stub runs in exactly one order, and the order is the whole story: gross pay, pre-tax deductions, taxes, post-tax deductions, net pay. Whatever comes out before the tax step shrinks the wages your tax is figured on. Whatever comes out after it does not. Two deduction lines of identical size, sitting on opposite sides of that step, cost you different amounts of take-home.
Here is the part most calculators quietly skip: a stub does not have one taxable-wage figure. It has two. Your W-2 prints them next to each other. Box 1 is your federal-income-taxable wages, and both flavors of pre-tax deduction pull it down. Boxes 3 and 5 are your Social Security and Medicare wages, and only Section 125 cafeteria dollars touch those. A traditional 401(k) deferral leaves Boxes 3 and 5 exactly where it found them, because the IRS counts elective deferrals as wages for FICA even while letting them skip income tax withholding.
Run the calculator's defaults and watch it happen. Gross pay $3,000 biweekly, $250 into a Section 125 health premium, $200 into a traditional 401(k), nothing post-tax, 22% combined income tax rate. FICA wages: $3,000 minus the $250 cafeteria premium = $2,750. Income-taxable wages: $3,000 minus $250 minus $200 = $2,550. Income tax is $2,550 x 22% = $561. Social Security is $2,750 x 6.2% = $170.50, Medicare is $2,750 x 1.45% = $39.88. Total tax $771.38, take-home $1,778.63. Now shove that same $450 into the post-tax bucket. Nothing shelters anything, tax on the full $3,000 jumps to $889.50, and the $118.13 that disappeared is what the word "pre-tax" was worth to you.
Which deductions are exempt from which taxes
This is the thing a single "pre-tax deductions" box cannot tell you. Section 125 cafeteria-plan deductions (health, dental, and vision premiums, HSA through payroll, health and dependent care FSA) escape federal income tax and Social Security and Medicare. Traditional 401(k), 403(b), and 457 deferrals escape federal income tax only. Both wear the same "pre-tax" label on the stub. They are 7.65 cents on the dollar apart.
| Deduction | Bucket | Federal income tax | Social Security & Medicare |
|---|---|---|---|
| Health / dental / vision premiums (Section 125) | Pre-tax | Exempt | Exempt |
| HSA through payroll (Section 125) | Pre-tax | Exempt | Exempt |
| Health FSA / dependent care FSA | Pre-tax | Exempt | Exempt |
| Qualified commuter / parking benefits | Pre-tax | Exempt | Exempt |
| Traditional 401(k) / 403(b) / 457 deferral | Pre-tax | Exempt | Taxable |
| Roth 401(k) | Post-tax | Taxable | Taxable |
| Union dues | Post-tax | Taxable | Taxable |
| Wage garnishment / child support | Post-tax | Taxable | Taxable |
| After-tax life / disability premiums | Post-tax | Taxable | Taxable |
| Charitable payroll giving | Post-tax | Taxable | Taxable |
The easiest way to hold all this in your head is price per dollar. Early in the year at a 22% rate, a dollar sent through a Section 125 plan costs you about $0.70 of take-home, because it ducks the 22% income tax and the 7.65% FICA. A dollar into a traditional 401(k) costs about $0.78, ducking the 22% alone. A post-tax dollar costs a full $1.00. One dollar leaving your paycheck, three different prices.
Before you conclude pre-tax always wins, look at disability premiums. Pay them with after-tax dollars and the benefit arrives tax-free if you ever have to claim it. Pay them pre-tax and the payout is taxable income, landing at the exact moment you are least able to absorb a tax bill. Sometimes the post-tax bucket is where a line belongs on purpose.
The Social Security wage base changes the answer late in the year
The 6.2% Social Security tax runs out at a wage base, $184,500 for 2026. Cross it with your YTD Social Security wages and the 6.2% simply stops for the rest of the year. Medicare has no such ceiling: it keeps taking 1.45%, plus another 0.9% on wages above $200,000 YTD. (Employers withhold that surtax at $200,000 no matter your filing status, so a married-joint couple under the $250,000 return threshold may see some of it come back at filing.)
Which means a cafeteria deduction is worth different money in January than in December. In January, a Section 125 dollar saves your income tax rate plus the full 7.65%. In December, if you are past the wage base, it saves your income tax rate plus 1.45%. The FICA edge over a 401(k) deferral collapses from 7.65 cents on the dollar to 1.45. It never quite vanishes, because Medicare never stops.
So the calculator asks for your YTD Social Security wages instead of guessing them from your per-period pay. Annualizing one paycheck has no way of knowing you started the job in March, took unpaid leave in the summer, or caught a fat bonus in Q2. Read the number off Box 3 of your latest stub, or rebuild it from your pay history with the YTD earnings calculator, which spits out the year-to-date figure this tool wants.
How to show pre-tax and after-tax deductions on a pay stub
Dump every deduction into a single "deductions" total and nobody reading the stub can reconcile it. Not a lender, not an auditor, and definitely not the employee standing at your desk asking why their 401(k) contribution did not lower their Social Security wages. The split this calculator works out has to make it onto the actual document.
Payslip44 tags every deduction line as Tax, Pre-tax, or After-tax, so the stub carries the distinction on its face. Save a deduction item template once (401(k), health premium, garnishment) and reuse it on every stub after that. Totals run on decimal money math, so a 6.2% line will not drift a cent over 26 paychecks the way a floating-point spreadsheet does. Finished stubs export to PDF, PNG, CSV, or plain text, and none of it leaves the device.
Download Payslip44 and itemize pre-tax and after-tax deductions on a real pay stub.
Estimates only. Actual withholding depends on your Form W-4, state and local rules, and your employer's plan design. This is not tax advice.
Frequently Asked Questions
Common questions about pre-tax vs post-tax deduction calculator
What is the difference between a pre-tax and a post-tax deduction?
A pre-tax deduction leaves gross pay before the tax math happens, so the wages your tax is calculated on are smaller. A post-tax deduction leaves after withholding, so it costs you take-home and buys you nothing on the tax side. Same dollar out of the paycheck, completely different result.
Does a 401(k) lower my taxable income?
Half of it. Your federal income taxable wages (W-2 Box 1) go down. Your Social Security and Medicare wages (Boxes 3 and 5) do not budge. The IRS still counts elective deferrals as wages for FICA, so every dollar you defer into a traditional 401(k), 403(b), or 457 plan gets hit for 7.65% on the way out.
Do pre-tax deductions reduce Social Security and Medicare taxes?
Section 125 cafeteria-plan deductions do: health, dental, and vision premiums, payroll HSA contributions, FSA contributions. Traditional retirement deferrals do not. So two lines on the same stub, both stamped "pre-tax," can be worth wildly different amounts to you. That is why this calculator makes you enter them separately.
Which deductions appear before taxes on a pay stub?
Gross pay, then pre-tax deductions, then taxes, then post-tax deductions, then net pay. That sequence is not a style choice, it is the arithmetic. A stub that runs the lines in some other order will not reconcile to net. If yours does not add up, redo it in that sequence and you will usually find the broken line.
Is a Roth 401(k) pre-tax or post-tax?
Post-tax. Roth money comes out of pay you have already been taxed on, and in exchange qualified withdrawals in retirement are tax-free. Traditional 401(k) is the mirror image: the break lands now, the tax bill lands later. Either way, put your Roth contribution in the post-tax field here.
Are HSA contributions FICA-exempt?
It depends how the money gets there. Through payroll under a Section 125 plan, yes: no federal income tax, no FICA. Moved in from your own bank account, you can deduct it at filing time, but the Social Security and Medicare tax was already taken out of that paycheck and nobody is giving it back. Payroll is the cheaper route, by 7.65%.
How much does a pre-tax deduction actually save me?
Roughly the deduction times your marginal rate. Take a $250 Section 125 health premium at a 22% income tax rate: $250 x (22% + 7.65%) = $74 saved. Move that same $250 into a traditional 401(k) and you save $250 x 22% = $55, because FICA still takes its cut. The calculator runs it against the real wage-base cap instead of pretending 7.65% applies all year.
Are pre-tax deductions always better?
No. A Roth contribution gives up the break today to buy tax-free income later. Disability premiums paid with after-tax dollars make the benefit tax-free if you ever have to claim it, which is exactly when you will care. Pre-tax wins this week's paycheck. Winning a paycheck and winning a lifetime are different games, and this calculator only plays the first one.