Calculator

Fast everyday maths, right in the page

Not every sum deserves a trip to a separate app or a phone unlock. This calculator is here for the small, frequent jobs: splitting a bill, working out a discount, adding up a few numbers, or checking a percentage before you commit to it. It supports the four basic operations along with brackets for grouping and a percent key, and it accepts input from your physical keyboard as well as the on-screen buttons, so you can type a quick calculation and press Enter without lifting your hands. Press Escape to clear and Backspace to fix a slip.

Getting percentages right

Percentages trip people up more than any other piece of everyday arithmetic, so it helps to keep the core ideas in mind. To find a percentage of a number, multiply by the percentage and divide by a hundred; fifteen percent of two hundred is two hundred times fifteen, divided by a hundred, which is thirty. To express one number as a percentage of another, divide the first by the second and multiply by a hundred. And to add a tax or a tip, work out the percentage and add it back to the original amount. The percent key here lets you fold those steps into a single expression rather than juggling them in your head, which is exactly what you want when a shop assistant is waiting or a bill needs settling.

Simple by design

There is a place for scientific calculators with dozens of functions, but most of the time what you actually need is speed and clarity. This tool keeps the buttons large, the screen readable, and the behaviour predictable, so there is nothing to learn before you start. Like the rest of the toolkit, it runs entirely in your browser, which makes it instant and means it works whether you are online or off. For maths that involves the calendar rather than plain numbers — ages, the gap between dates, business days, or a countdown to an event — reach for the dedicated time tools, which understand weekends and leap years in a way an ordinary calculator never could.