Everyday calculators

Dates, time and numbers you check every week. Seven calculators, each with the answer at the top and the method underneath.

32yAge calculatorYour exact age in years, months and days — and how long until your next birthday.↔Days between datesThe exact number of days between two dates, and how many of them are working days.%Percentage calculatorThree percentage questions, answered without guessing which formula applies.8hHours calculatorHours worked between two clock times, minus breaks, in decimal and h:mm.−25Discount & sales tax calculatorThe sale price, the tax added, or the net price hidden inside a gross one.mpgFuel cost calculatorWhat the trip costs, what each passenger owes, and how much fuel it burns.3:4Ratio calculatorFind the missing term in a proportion, or reduce a ratio to its simplest form.

What counts as an everyday calculation

These are the small sums that show up in the middle of a normal week: how old you are on a form, how many days until a deadline, what a jacket costs after a discount, how many hours you actually worked, how much fuel a trip needs. None of them need an account or a spreadsheet, and all of them are easy to get wrong by a day or a percentage point.

Each calculator here follows the same order. The result appears first, updating as you type. Under it you get the formula, a worked example with real numbers, and the edge cases that change the answer — leap years, month lengths, working days, tax applied before or after a discount.

Why the method is shown

A number without a method is hard to trust and impossible to check. If a payroll system disagrees with our hours calculator, you need to see whether it is counting breaks, rounding to the nearest quarter hour, or using a different week start. Showing the working makes that comparison possible — and it is also the honest way to publish a calculator.

Coming next

Age and the rest of the set are being written in six languages: English, Turkish, German, Portuguese, Italian and Spanish. Each language gets its own URL, its own worked example and its own local date and number formatting, rather than a machine translation of this page.