Federal tax brackets work on your paycheck through a projection: your employer takes what you earn in a single pay period, multiplies it out to an annual salary, subtracts your standard deduction and pre-tax contributions, runs that taxable amount through the marginal brackets, and then divides the resulting yearly tax back down to the size of your check. The brackets themselves are annual thresholds set by the IRS, ranging in 2026 from 10% on the first $12,400 of taxable income for a single filer up to 37% on income above $640,600.1Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026 What lands on your stub is an estimate of your share of that annual bill, spread across the year.
The Annualization Math Behind Each Check
Payroll software doesn’t know what you’ll actually earn for the year, so it guesses based on the check in front of it. Earn $2,500 on a biweekly pay period, and the system assumes you’ll make $65,000 over 26 pay periods.2Internal Revenue Service. Publication 15-T Federal Income Tax Withholding Methods From that projection it subtracts your annualized standard deduction, applies the marginal rates to what remains, arrives at a full year’s tax, and divides by 26 to get the federal income tax line for that specific check.
The projection resets every pay period. A week of overtime pushes your projected annual income higher, sometimes into a bracket you wouldn’t actually hit for the year, and the withholding on that check jumps to match. The next normal check drops back down. Nothing about your real annual tax rate changed; the estimator just extrapolated from a single data point that happened to be larger than usual.
2026 Marginal Rates and How They Stack
Brackets are marginal, meaning each rate applies only to the slice of income inside it. The 2026 thresholds for single filers and married couples filing jointly:1Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026
- 10%: up to $12,400 single; up to $24,800 joint
- 12%: $12,401 to $50,400 single; $24,801 to $100,800 joint
- 22%: $50,401 to $105,700 single; $100,801 to $211,400 joint
- 24%: $105,701 to $201,775 single; $211,401 to $403,550 joint
- 32%: $201,776 to $256,225 single; $403,551 to $512,450 joint
- 35%: $256,226 to $640,600 single; $512,451 to $768,700 joint
- 37%: over $640,600 single; over $768,700 joint
A single filer with $60,000 in taxable income pays 10% on the first $12,400, 12% on the portion from $12,401 to $50,400, and 22% only on the remaining $9,600. Your payroll system runs exactly this layered arithmetic every period using the annualized projection, which is why the amount on the “federal income tax” line rarely matches any single bracket rate cleanly.
How Your Filing Status Changes the Calculation
The filing status you enter on your W-4 is the biggest lever in the whole calculation. It sets both the width of each bracket the software uses and the standard deduction it subtracts up front.
Married filing jointly brackets run roughly double the width of single brackets at most levels. A single filer hits the 22% rate at $50,401 of taxable income; a joint filer doesn’t reach it until $100,801.1Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026 The standard deduction moves the same way: $16,100 single versus $32,200 joint for 2026. Picking joint on your W-4 with the same paycheck produces meaningfully less withholding than single.
Head of household sits between the two. If you’re unmarried and cover more than half the cost of a home for a qualifying dependent, the 2026 standard deduction is $24,150, and the 12% bracket runs up to $67,450 before 22% starts. Single parents who default to “single” on the W-4 often over-withhold all year because of this.
The standard deduction is baked into every paycheck, not saved for tax season. The software subtracts the annualized deduction from your projected income before brackets touch it. A single filer projected to earn $55,000 has $16,100 removed, leaving $38,900 for the brackets to work on. That’s why your effective withholding rate always runs below the top bracket your income reaches.
Pre-Tax Deductions Come Off Before the Brackets
Certain payroll deductions reduce the income the brackets ever see. The more you route through them, the smaller the taxable base on each check.
- Traditional 401(k) and 403(b) contributions are excluded from federally taxable wages at the moment of deferral. Defer $300 from a $3,000 check and the brackets apply to $2,700. Roth 401(k) contributions come out of after-tax pay and don’t reduce withholding.3Internal Revenue Service. 401(k) Plan Overview
- Employer health insurance premiums typically flow through a Section 125 cafeteria plan, so the salary reduction happens before federal income tax is calculated.4Internal Revenue Service. FAQs for Government Entities Regarding Cafeteria Plans
- Healthcare and dependent care FSA contributions run through the same Section 125 mechanism and reduce taxable gross each period.
- Payroll HSA contributions are pre-tax if you’re in a qualifying high-deductible plan. The 2026 caps are $4,400 self-only, $8,750 family, plus a $1,000 catch-up if you’re 55 or older.5Internal Revenue Service. Revenue Procedure 2025-19
If you raise your 401(k) deferral or start a new benefit mid-year, the federal income tax line on your next stub should drop, because the base the brackets multiply against just got smaller.
Why a Bonus Check Looks Taxed Harder
Bonuses, commissions, and severance are supplemental wages, and employers get to withhold on them differently. Most use the flat-rate method: a straight 22% on supplemental payments up to $1 million in a calendar year, and 37% on any excess above that.6Internal Revenue Service. Publication 15, Employer’s Tax Guide The alternative aggregate method combines the bonus with your regular pay and runs the total through the standard bracket calculation, which often withholds even more because the combined check annualizes into a higher bracket.
Either method is only an estimate. If more came out than your actual marginal rate for the year justifies, you get it back at filing. If less, you owe the difference.
Using Your W-4 to Adjust What Comes Out
Form W-4 is the one page that tells your employer how to calibrate all of the above. Step 1 sets your filing status. Step 2 handles multiple jobs or a working spouse so the combined income is accounted for and neither job under-withholds. Step 3 reduces withholding for dependents: $2,200 for each qualifying child under 17 in 2026, and $500 for each other dependent.7Internal Revenue Service. Form W-4 – Employee’s Withholding Certificate Step 4 is for fine tuning: outside income in 4(a), extra deductions beyond the standard amount in 4(b), and a flat additional dollar amount per check in 4(c).
The 4(c) line is the simplest way to correct a shortfall. If you freelance on the side or want a bigger refund, adding $50 or $100 per paycheck avoids the math of estimating how outside income shifts your brackets. The IRS Tax Withholding Estimator can suggest a number based on your whole picture.8Internal Revenue Service. Tax Withholding Estimator You can submit a new W-4 to your employer at any time, and the change generally takes effect within a pay cycle or two.
If you had zero federal income tax liability last year and expect none this year, you can claim exempt on the W-4 by checking the exempt box and skipping Steps 2 through 4. The claim expires annually; a 2026 exemption requires a new form by February 16, 2027, or the employer defaults you to single with no adjustments.7Internal Revenue Service. Form W-4 – Employee’s Withholding Certificate
What Else Comes Out That Isn’t Bracket-Based
Federal income tax is only one of the federal lines on your stub, and the others don’t follow bracket logic at all. Social Security is a flat 6.2% on wages up to $184,500 in 2026; once you cross that ceiling, the line disappears for the rest of the year and your take-home rises.9Social Security Administration. Contribution and Benefit Base Medicare is 1.45% on all wages, with an added 0.9% surtax on wages above $200,000 in a calendar year. Neither is affected by your W-4.
State income tax, where it exists, runs on its own brackets and filing statuses that don’t always mirror the federal ones. Nine states — Alaska, Florida, Nevada, New Hampshire, South Dakota, Tennessee, Texas, Washington, and Wyoming — don’t impose a broad-based income tax on wages, so paychecks there face only federal withholding and FICA.