What this site calculates
Money questions that cross a border or a tax bracket rarely have a quick answer. What does an offer in another country actually pay once its tax office is done? What does a raise leave after the bracket it pushes you into? What does an employer really spend to put a salary in your account? Each of those is a calculator on this site, or is on its way to being one.
The starting point is take-home pay, because every other figure sits on top of it. Enter a gross salary for a country or a US state and you get the payslip breakdown: income tax, social insurance or payroll contributions, the net figure for the year and for the month, and what the employer pays on top.
Where the numbers come from
Every tax parameter on this site is read out of an official document: the revenue service of a country, or the department of revenue of a US state. Each data file records the document it came from and the date it was last checked, and both are shown on the page that uses it. Nothing is estimated, and nothing is written from memory.
The same rules are implemented twice, once on the server and once in the browser, and both are tested against fixtures taken from official tables. If the two ever disagreed the tests would fail before the page shipped. That is the reason a calculator here can be fast without being loose about the numbers.
Keep rate, and why it is shown first
Most calculators lead with an effective tax rate. The number people actually want is the other side of it: the share of the salary that stays with them. This site calls that the keep rate and shows it alongside the standard effective rate, never instead of it, so the figure is easy to quote without being misleading.
What is not here
There is no sign-up, no account and no saved history. The salary you type is used to produce the page you asked for and is kept out of the server access log. Results are estimates for comparing options, not tax advice or a substitute for a payslip, and they assume the standard withholding case for the jurisdiction unless you change the options on the page.