The most common message this site receives is some version of: “Your page says my bi-weekly take-home on $100,000 in Austin is $3,045, but my pay stub says $2,9xx.” Both numbers are right. They are answers to different questions, and the difference is the single most useful thing to understand about a U.S. paycheck.
Liability: what you owe for the year
The audits on this site compute your annual tax liability — the total federal, FICA, state and local tax due on a salary for a full year, under a specific set of assumptions (single filer, standard deduction, no dependents, no other income) — and divide it by the number of pay periods. On $100,000 in Austin that is $13,170 of federal income tax and $7,650 of FICA, a net of $79,180, or $3,045 per bi-weekly check across 26 checks. This is the number you would arrive at when you file your return, if the assumptions hold.
Withholding: what your employer takes each check
Your employer does not know your annual liability. It knows your salary, your pay frequency and what you told it on Form W-4, and it uses the IRS withholding tables to estimate a per-check amount. The tables are designed to get close to the liability for a typical filer, but four things routinely push them away from it:
Your W-4 entries. Filing status, the multiple-jobs checkbox, dependents claimed, other income, deductions and any extra withholding amount all move the per-check figure. Someone who checked the multiple-jobs box on a single job will be over-withheld all year; someone who claimed dependents they no longer have will be under-withheld.
Pre-tax deductions on the stub. Health premiums, 401(k) contributions, HSA and FSA deposits, commuter benefits — all reduce taxable wages, and the audit’s baseline assumes none of them. This is the largest and most legitimate source of difference. The slider on every audit exists to close it.
Bonuses and irregular pay. Supplemental wages are typically withheld at a flat 22% federal rate regardless of your bracket. A bonus check on a $60,000 salary is over-withheld (the marginal rate is 12%); a bonus on a $250,000 salary is under-withheld (32%). Both are settled at filing.
Mid-year starts and raises. The tables assume the current check’s pay continues for the whole year. Start in July on $100,000 and the tables withhold as though you will earn $100,000 that year, when you will earn $50,000; you will be over-withheld and get a refund.
Which one is right?
Liability is the true cost. Withholding is a running estimate of it. If withholding runs high you get the difference back as a refund the following spring — an interest-free loan to the Treasury. If it runs low you owe the difference, and if it is low enough there can be an underpayment penalty. The goal is for the two to match, and the tool for that is the W-4.
How to bring them together
Use the IRS Tax Withholding Estimator once a year, and after any raise, marriage, new dependent or second job. It takes your year-to-date stubs and tells you what to enter on a new W-4. If the audit here shows a monthly take-home noticeably higher than your stub, and you have no pre-tax deductions, the likeliest explanation is an over-withholding entry on your W-4 — and the fix is a form, not a negotiation.
What the audit is for
Not to predict your stub, which depends on choices only you know. It is the reproducible floor: the least you will net from that salary in that place, under standard assumptions, with every line itemized and sourced. Compare your stub to it, account for your own deductions with the slider, and what remains is the withholding gap — which is either a refund in waiting or a W-4 to fix.
Audits cited in this guide
Open the full paycheck breakdowns
About the figures in this guide
Every dollar amount above is produced by the same deterministic tax engine that generates the audit pages, using the published 2026 federal brackets and standard deduction, the 2026 Social Security wage base, each state's published schedule and each city's local tax rules. Assumptions: single filer, standard deduction, no dependents, no itemized deductions. Rent figures are median 1-bedroom asking rents refreshed quarterly. Read the methodology, or send a correction with a primary source.