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Accuracy: our calculator vs. the IRS tables

Every time the site is built, our federal withholding engine is checked against the official IRS tables. Right now 1,062 of 1,062 values match to the dollar.

What we test

IRS Publication 15-T (2026) prints a Wage Bracket Method table for biweekly payrolls: for each $10 or $20 range of wages, it gives the federal income tax to withhold for single, married filing jointly and head of household employees, with and without the Step 2 (two jobs) box checked. These tables are built from the IRS percentage method applied at the middle of each range, so a correct engine must reproduce every cell.

We take the 177 wage ranges of that table, run the middle of each range through the same code that powers our paycheck calculator, round to the dollar and compare. Six values per row gives 1,062 comparisons.

Sample of the comparison

Biweekly wages	Single: IRS	Single: ours	Married jointly: IRS	Married jointly: ours	Head of household: IRS	Ours
$310–$320	$0	$0	$0	$0	$0	$0
$430–$440	$0	$0	$0	$0	$0	$0
$550–$565	$0	$0	$0	$0	$0	$0
$730–$745	$12	$12	$0	$0	$0	$0
$910–$925	$30	$30	$0	$0	$0	$0
$1,090–$1,105	$48	$48	$0	$0	$17	$17
$1,270–$1,285	$69	$69	$4	$4	$35	$35
$1,505–$1,525	$98	$98	$28	$28	$59	$59
$1,745–$1,765	$127	$127	$52	$52	$86	$86
$1,985–$2,005	$156	$156	$76	$76	$114	$114
$2,225–$2,245	$184	$184	$101	$101	$143	$143
$2,525–$2,555	$221	$221	$137	$137	$180	$180
$2,885–$2,915	$298	$298	$180	$180	$223	$223
$3,245–$3,275	$378	$378	$224	$224	$266	$266
$3,605–$3,635	$457	$457	$267	$267	$319	$319

One row in twelve shown, Step 2 box unchecked. The full test also covers the checked box and runs automatically before each update.

Other checks

Social Security: 6.2% stops at the 2026 wage base of $184,500 (maximum $11,439).
Medicare: 1.45% of all wages plus 0.9% above $200,000.
No Tax on Tips and No Tax on Overtime: limits and the $100-per-$1,000 phase-out follow Schedule 1-A line by line, including the IRS’s own $20-an-hour overtime example.
State income tax: spot checks of flat-rate states, exemptions and zero-bracket thresholds.

What we do not claim

State figures are annual estimates spread evenly across paychecks, not each state’s own withholding tables, and local taxes are not included unless a page says so. Your actual withholding also depends on your Form W-4 and your employer’s payroll system. If you find a difference, please tell us through the contact page; corrections are dated on the methodology page.

Last checked November 2026. Source: IRS Publication 15-T (2026).