FastCalcs

About FastCalcs

FastCalcs makes free calculators that answer one question each, quickly and clearly. You type your numbers, you get the answer straight away, and you can see exactly how it was worked out.

Why we built it

Most people meet a calculation at an awkward moment: at the dealership, in the paint aisle, or late at night comparing mortgage offers. Too many calculator sites are slow, cluttered, or give an answer with no explanation. We wanted the opposite: a page that loads instantly, works on any phone, and shows its working so you can trust the number.

What you’ll find here

We add new calculators every month, based on what people ask for.

How we work

  • Formulas from trusted sources. Health calculators follow published research and public health agencies such as the CDC. Financial calculators use standard lending formulas and, where relevant, official rules such as those from the US Consumer Financial Protection Bureau. Each page lists its sources.
  • Tested before anything goes live. Every calculator is checked against hand-worked answers and more than 1,000 generated test cases. See how we check our formulas.
  • The working is always shown. Every page explains the formula and walks through a real example.
  • Plain language. No jargon without an explanation, and no fine print hiding the answer.

What we promise

  • Free, with no account. Every calculator works without signing up.
  • Private by design. Your numbers stay on your device. Read about our data and security.
  • Independent. No one pays us to change a result, and we will never rank or present a product as a calculator result.
  • Honest about limits. The math is exact, but real life can differ, and we say so. Our disclaimer explains what each calculator can and can’t tell you.
  • Accessible. Pages work with a keyboard and screen readers, adapt to light and dark mode, and respect reduced-motion settings.

Get in touch

Spotted a mistake, have an idea, or want a calculator we don’t have yet? Email hello@fastcalcs.app or visit our contact page. Every message is read.