About Calculate.FAST
Calculators that show their working — so you can trust the answer, not just read it.
Most online calculators hand you a number and hide everything behind it. Calculate.FAST does the opposite: every serious calculator shows its assumptions, the formula it used, a worked example, its limitations, and dated sources — right beside the result.
How it works
Calculations happen in your browser. Rule-based calculators — like income tax — state the period they cover, and we update them promptly when new official figures are published.
Part of the Files.FAST Network
Calculate.FAST is part of the Files.FAST Network, operated by Files Fast. The network includes tools that convert, compress and extract files, while Calculate.FAST is the place for working things out.