Why gross pay and take-home pay are so far apart
Your net paycheck is what remains after four different systems have taken a share, and each one measures your pay differently. That is the whole reason the gap feels unpredictable: there is no single "taxable pay" figure that everything is applied to.
Federal income tax is charged on gross less pre-tax benefits and retirement deferrals. Social Security and Medicare are charged on gross less pre-tax benefits but not less retirement deferrals. State income tax usually follows the federal base but not always — Pennsylvania, for one, taxes 401(k) deferrals at the state level while exempting them federally. Post-tax deductions come out of what survives all of it, and reduce your pay without reducing any tax at all.
Getting the order right matters more than getting any single rate right. Move $200 a period from a post-tax Roth deferral into a traditional pre-tax deferral and your take-home pay changes by far less than $200, because the pre-tax version cuts your income tax at the same time. That kind of trade is what this calculator is for: change one line, and watch which of the other lines move with it.
The five deduction layers, in the order payroll applies them
Layer one: section 125 pre-tax benefits. Health, dental and vision premiums taken through a cafeteria plan, health and dependent care FSA contributions, and HSA contributions made by payroll deduction. These reduce every tax base — federal, state, Social Security and Medicare. That triple exemption is why the same HSA dollar is worth about 7.65% more through payroll than by personal cheque.
Layer two: retirement deferrals. Traditional 401(k), 403(b) and 457(b) deferrals reduce income tax wages only. FICA is still charged on them, and it always will be — this is not an oversight but the design, since retirement deferrals must still earn Social Security credits. A Roth deferral reduces nothing and belongs in the post-tax layer.
Layer three: federal income tax. Publication 15-T's percentage method annualises what is left, applies your W-4 entries, looks up the annual table and divides back down. The federal income tax withholding calculator shows that step in full detail.
Layer four: FICA and state or local tax. Social Security takes 6.2% up to the annual wage base and Medicare takes 1.45% with no cap, both on the layer-one base. State income tax varies from nothing at all in nine states to graduated schedules above 10%; enter your effective rate, not your top bracket, since most states apply a standard deduction and their own brackets. City wage taxes in places such as Philadelphia, New York City and much of Ohio sit on top.
Layer five: post-tax deductions. Roth contributions, union dues, voluntary life and disability premiums, and wage garnishments. These reduce cash and nothing else. A garnishment is the exception with its own rules — federal law caps most consumer garnishments by reference to disposable earnings, which the wage garnishment calculator works through.
Worked example: $2,000 biweekly with a 5% deferral and $200 of premiums
You earn $2,000 every two weeks, single on your W-4 with no credits, defer 5% to a traditional 401(k), pay $200 of health premiums through a cafeteria plan, and live in a state with a 5% flat effective rate.
- Section 125. $200.00 comes off first.
- Retirement deferral. 5% of $2,000 = $100.00.
- FICA wages. 2,000 − 200 = $1,800.00. The deferral does not reduce this.
- Income tax wages. 1,800 − 100 = $1,700.00.
- Federal withholding. Annualise: 1,700 × 26 = $44,200. Subtract the single deduction credit of $8,600 to get an adjusted annual wage of $35,600. That lands in the 12% row starting at $18,325 with a base of $1,192.50, so 1,192.50 + 0.12 × (35,600 − 18,325) = 1,192.50 + 2,073.00 = $3,265.50 a year, or 3,265.50 ÷ 26 = $125.60 per check.
- Social Security. 1,800 × 0.062 = $111.60.
- Medicare. 1,800 × 0.0145 = $26.10. FICA total $137.70.
- State tax. 5% × 1,700 = $85.00.
- Net pay. 2,000 − 200 − 100 − 125.60 − 137.70 − 85.00 = $1,351.70, which is 67.6% of gross.
Now test the trade. Raising the deferral from 5% to 10% adds $100 of deferral. Income tax wages fall to $1,600, so annualised wages fall by $2,600 and federal withholding falls by 0.12 × 2,600 ÷ 26 = $12.00 per check; state tax falls by 5% × 100 = $5.00. FICA does not move at all. Net pay therefore falls by 100 − 12.00 − 5.00 = $83.00, not $100. You put $100 into the account and $83 left your paycheck — at a 12% federal marginal rate. At a 22% marginal rate the same $100 deferral would cost $73 of take-home pay.
Which deductions reduce which tax
| Deduction | Federal income tax | Social Security & Medicare | Typical state treatment |
|---|---|---|---|
| Health, dental, vision premiums (section 125) | Reduces | Reduces | Reduces |
| Health FSA and dependent care FSA | Reduces | Reduces | Reduces |
| HSA by payroll deduction | Reduces | Reduces | Reduces in most states |
| Traditional 401(k) / 403(b) deferral | Reduces | No effect | Reduces in most states |
| Roth 401(k) deferral | No effect | No effect | No effect |
| Qualified transit and parking benefits | Reduces | Reduces | Reduces in most states |
| Union dues, voluntary life, garnishments | No effect | No effect | No effect |
| Group-term life above $50,000 (imputed) | Increases | Increases | Increases |
State treatment is the common pattern, not a rule. Pennsylvania taxes 401(k) deferrals; New Jersey taxes several items the federal system exempts. Check your state's withholding guide before relying on the last column.
What take-home percentage is normal, and when to worry
For a single filer on a middle income with modest benefits, take-home pay typically lands somewhere between 65% and 80% of gross. The spread comes almost entirely from three things: your state, your marginal federal bracket, and how much you are voluntarily diverting into benefits and retirement. A 15% deferral rate can lower your take-home percentage by more than a move from a no-tax state to a high-tax one, and only one of those is money you lost.
Read the breakdown table rather than the headline percentage. Money in the pre-tax rows is still yours — it went into your HSA or your retirement account. Money in the tax rows is gone until you file. A paycheck showing 62% take-home with 12% going into retirement is in a much better position than one showing 70% with nothing saved.
The changes worth investigating are the ones you did not cause. Federal withholding rising with no W-4 change usually means an extra pay period in the month, a bonus inside the period, or imputed income being added. FICA rising above 7.65% of visible gross means taxable fringe benefits were added to your wages. Social Security disappearing entirely means you crossed the wage base — permanent for the rest of the year, and worth checking against the FICA payroll tax calculator. State tax changing on its own usually means a new rate table took effect in January.
If you are comparing a job offer, do the comparison annually rather than per period, and be careful with pay frequency. A semimonthly employee gets 24 larger checks and a biweekly employee gets 26 smaller ones on the same salary; the annual total is identical but the monthly cash flow is not, since two months a year contain three biweekly checks. The pay period conversion calculator handles that translation, and the salary to hourly rate calculator converts between a salary offer and a contract rate.
Assumptions and limits of this calculator
- No year-to-date tracking. Every period is computed independently, so the Social Security wage base and the additional Medicare tax threshold are flagged in warnings rather than applied. Late-year paychecks for high earners will differ.
- State tax is a flat effective rate. Real state withholding uses its own tables, allowances and standard deductions. Enter an effective rate taken from a recent pay stub for the closest result.
- Supplemental wages are not separated. Bonuses withheld at the flat 22% federal supplemental rate will not match the table method used here.
- Employer contributions are excluded. The employer's 7.65% FICA match, retirement match and share of your health premium are real costs of employing you but never appear in a net pay calculation.
- Post-tax deductions are taken as entered. Real garnishments are capped by reference to disposable earnings and yield to higher-priority orders such as child support.
- Pre-2020 Forms W-4 are not modelled. Employees still on an allowance-based W-4 are withheld from a different set of tables.
Reconcile against a real stub before you trust any projection
Take one recent pay stub and enter its gross, deductions and pay frequency here. Federal withholding should land within a dollar or two if your W-4 matches what you entered; FICA should match to the cent unless imputed income is present. If federal withholding is close but FICA is not, look for a taxable fringe benefit. If FICA is exact but federal withholding is far off, the W-4 on file is probably not what you think it is — ask payroll for a copy. Once the stub reconciles, projections from this page are reliable for the rest of the year.
Using this to make decisions rather than just to check a stub
The most valuable use of a net pay model is testing a change before you make it. Three come up repeatedly.
Raising a retirement deferral. The cost to take-home pay is always less than the amount deferred, by exactly your combined marginal income tax rate. At a 22% federal and 5% state rate, $100 deferred costs $73 in cash. Test the specific number rather than assuming, because a deferral that pushes you down a bracket has a slightly larger effect than the flat calculation suggests.
Switching a health plan. A high-deductible plan with a lower premium raises take-home pay by the premium difference less the tax the premium was sheltering. Since section 125 premiums escape income tax and FICA, the take-home gain is only about 70% of the premium saved for a typical filer, which has to be weighed against a higher deductible. The HDHP vs PPO total cost calculator models the full comparison including expected claims.
Fixing a refund or a balance due. Do not adjust your filing status to move withholding. Use Step 4(c) extra withholding to add, or Step 3 credits you genuinely qualify for to subtract. Both are transparent and reversible; a mis-stated filing status is neither, and it produces a withholding pattern nobody can explain a year later.
One caution about gross-ups. If an employer promises you a specific net amount — a relocation payment or a spot bonus, say — the gross needed is not the net divided by one minus the tax rate, because the tax on the gross-up is itself taxable. That circularity has its own closed-form solution, handled by the payroll gross-up calculator.