Changelog
Updated
Changes that could affect a number you got from this site: a figure verified, a rule newly modelled, a mistake corrected. Refactors and design work are not here. They are in the repository and they do not change your answer.
This page, and an index of the calculators
Added a changelog so changes to the figures are visible without reading the repository, and a calculator index. Cookieless analytics was wired in but is not running: no measurement script is loaded and nothing leaves this site's server. When it is switched on it will record which page was visited and never what was entered. The code that strips your figures out of the address is tested, and the privacy page says so.
The Medicare surtax gap on RSU vests
The RSU calculator now models a second shortfall it previously declared out of scope: the 0.9% Additional Medicare Tax. Your employer withholds it against a flat $200,000 of its own payroll while you owe against your filing status and every wage on your return. Wages it cannot see go unwithheld and are settled at filing: a second job, a previous employer, a spouse's on a joint return. Omitting it understated the total for exactly the people the tool is for.
2026 federal tax and Social Security figures verified
Every 2026 figure used on this site was read from its primary document and checked by a person: the IRS Revenue Procedure for the rate tables and standard deduction, Publication 15 for supplemental wage withholding, the Social Security Administration's cost-of-living fact sheet for the FICA rates and wage base, and the tax code itself for the Additional Medicare thresholds. Until that was done the calculator showed no results at all rather than unverified ones.
Corrections
Nothing published here has needed correcting yet. When something does, it will be listed above with what was wrong, what it is now, and when it changed. A site that quietly rewrites its own figures is not one you can check. Our editorial policy sets out the process, and if you think a figure is wrong, tell us.