Math Calculators

The math calculators here handle everyday arithmetic that's easy to get wrong by hand: what percentage one number is of another, a percentage increase or decrease, or working backward from a percentage change to the original value — each with the formula shown next to the result.

Percentage change trips people up most often, since increasing a number by 20% and then decreasing it by 20% doesn't return the original value — the base changes between the two steps.