How we calculate

Every number comes from an official rule, written as code and tested against the agency’s own published values before each release.

Paychecks

Federal withholding follows IRS Publication 15-T (2026), Worksheet 1A, line by line, and is checked against every amount in the IRS’s printed 2026 withholding tables (4,794 values). Social Security stops at $184,500 of pay; the extra 0.9% Medicare tax starts at $200,000. Each state follows that state’s own 2026 withholding formula and is tested against that state’s published examples.

Your tax year

The refund-or-bill estimate follows the 2026 brackets, standard deductions and credits in IRS Revenue Procedure 2025-32, including the child tax credit, the earned income credit, and the tips, overtime and senior deductions.

Working for yourself

Self-employment tax follows Schedule SE; the 20% small-business deduction follows Form 8995 (with the $400 minimum that starts in 2026); quarterly payments follow Form 1040-ES. Mileage uses the IRS business rates for 2026: 72.5¢ a mile through June and 76¢ from July 1. State income tax for contractors is included only where that state’s 2026 rules are confirmed; elsewhere the page says so.

Rates we refresh

Savings and mortgage rates come from the FDIC national savings rate and the Freddie Mac weekly mortgage survey, via the Federal Reserve Bank of St. Louis (FRED), refreshed at each release.

What we don’t do

We don’t guess. When a case isn’t covered, a state’s rules aren’t published yet, or a number depends on something we can’t know, the page says so instead of showing a figure.

Last verified November 5, 2026.