Calculators that show their work
Type your numbers and the result updates instantly. Below every calculator you will find the formula, a worked example and the cases where people usually get it wrong.
- Age CalculatorEnter your date of birth to see your exact age in years, months and days, your age in total days and weeks, and the days until your next birthday.
- Percentage CalculatorFind a percentage of a number, what percent one number is of another, and the percent increase or decrease between two values, with formulas.
- Discount CalculatorEnter the original price and the percent off to see the sale price and how much you save, or find the discount rate from two prices. Stacked discounts too.
- Overtime CalculatorEnter your hourly rate and weekly hours to see regular pay, time and a half overtime pay and total weekly gross pay under the federal 40-hour rule.
- Date CalculatorCount the days, weeks and business days between two dates, or add and subtract days from a date to find the result with its weekday.
- Time Duration CalculatorFind the hours and minutes between two times, including shifts that pass midnight, in decimal hours too. Or add and subtract time from a clock time.
How these calculators are built
Each calculator runs entirely in your browser. Nothing you type is sent to a server or stored, so you can enter real salaries, dates and prices without creating an account. Results update as you type, and the page below the calculator spells out the exact formula it uses, so you can check the math by hand.
Where a rule comes from law or an official body, such as the 40-hour overtime threshold under the Fair Labor Standards Act, the page links to the primary source rather than a summary. Every page shows the date it was last reviewed. If you spot a result that looks wrong, the contact page explains how to reach us.