We started Key Calculators because we kept running into the same problem: we would search for a simple calculation — interest on a deposit, roofing material for a repair, what a repipe job should roughly cost — and land on a page buried in ads, with a result and no explanation of where the number came from. No formula, no source, just a box asking me to trust it.

So this site does the opposite. Every calculator here shows its formula on the page. If a number is an estimate rather than an exact figure, it says so, and explains why. Where a calculator relies on industry data rather than a fixed mathematical formula — the repiping cost calculator, for instance — We cross-check it against several independent sources before publishing, not just one.

What’s here right now

Key Calculators is new, and we would rather say that plainly than pretend otherwise. There are a few calculators live at the moment, with more being added as each one is researched and built properly rather than rushed out. We would rather have ten calculators we trust than a hundred we don’t.

How a calculator gets built

Each one starts from a real question — usually one we have searched for ourselves, or one someone’s asked us to add. We find the underlying formula or the best available cost data, check it against more than one source where the numbers aren’t a fixed equation, and only publish once we can explain exactly how the result was reached. That explanation stays on the page permanently, not hidden behind a “how it works” link nobody clicks.

Get in touch

If a calculator gave you a strange result, if you spotted an error, or if there’s a specific calculation you can’t find anywhere else, the contact page reaches us directly. We read everything that comes through it.