Why these tools
Most free calculators online don't tell you where their tax rates come from or when they were last updated. Ours do. Each tool states its official source — the European Commission's tax database, the Canada Revenue Agency, GOV.UK — with the effective dates and the date we last verified the data. If a dataset hasn't been re-verified recently, the page tells you that too, instead of quietly serving stale numbers.
The formulas behind every tool are documented on the tool's own page with a worked example, so you can check our arithmetic by hand. If you spot something wrong, tell us — corrections are published under our editorial policy.