Everyday math calculators and guides
Some calculations are too small to pay attention to and too easy to get wrong: a discount, a percentage change, an age on a form.
Calculators and tools
Guides and explainers
Math
How to calculate percentages (with the three formulas)
Percentages run on three formulas — percent of a number, percentage change, and what percent A is of B. Learn them once and you can price discounts, read margins, and check any claim in seconds.
MathHow to calculate your exact age (in years, months, and days)
Your age is not just a number of years. Here's how to work out your exact age in years, months, and days — and why the odd-looking math actually matters.
These tools do the arithmetic instantly and show the working. The guides explain the formulas and the mistakes they prevent, so you can sanity-check any number before you rely on it.