Math & Percentage Calculators

Some calculations are too quick to open a spreadsheet for, and too easy to get subtly wrong in your head — a tip split, a percentage off, a recipe scaled for eight instead of four. This is the corner of CalcNotebook for the everyday math that comes up between the big decisions.

Here you'll find the tools people reach for most: working out a percentage of a number (or the percentage change between two), simplifying and comparing fractions, converting between units of length, weight and temperature, and generating genuinely random numbers when you need one. Each tool runs entirely in your browser — nothing you type is sent to a server — and each one shows the formula it used, so you leave understanding the answer rather than just copying it.

Whether you're a student checking homework, a shopper decoding a sale, a cook scaling a recipe, or just someone who likes their numbers to be right, these calculators are free, fast, and clutter-free — no sign-up, ever. Every result is yours to keep: copy it as text, or share a link that reopens the calculator with the same numbers filled in.