Calculators
Everyday sums, done properly and shown with the formula behind them.
Fifteen calculators for the numbers people most often work out by hand: splitting a restaurant bill, checking a sale price, estimating a loan payment, projecting savings, working out a GPA, or counting the days to a date. Results update as you type, and every page explains the formula it uses and includes a reference table worked out with the same code, so you can check the answer against a second source.
Tip Calculator
Tip, total, and each person’s share.
Age Calculator
Exact age in years, months, and days.
Percentage Calculator
X% of Y, what percent, percent change.
GPA Calculator
Credit-weighted GPA on the 4.0 scale.
Days Until Calculator
Count the days to or since any date.
BMI Calculator
Body mass index, metric or imperial.
Discount Calculator
Sale price and how much you save.
Pregnancy Due Date Calculator
Estimated due date and current week.
Time Duration Calculator
Hours and minutes between two times.
Loan Payment Calculator
Monthly payment and total interest.
Compound Interest Calculator
Savings growth with monthly deposits.
Calorie Calculator
BMR and daily calorie needs.
Unit Converter
Length, weight, and temperature.
Pace Calculator
Running pace, speed, and finish times.
Sales Tax Calculator
Tax amount and total price.
Money
The tip, discount, sales tax, and percentage calculators cover shopping and eating out. The loan payment calculator uses the standard amortization formula behind most car, personal, and mortgage loans, and the compound interest calculator projects a savings balance month by month with regular deposits.
Health and fitness
The BMI calculator uses the WHO adult ranges. The calorie calculator uses the Mifflin-St Jeor equation for resting energy use and standard activity multipliers. The pace calculator turns a distance and time into pace per mile or kilometer and projects race finish times. The due date calculator applies Naegele's rule. These give estimates for planning; they are not medical advice.
Dates, time, and units
The age and days until calculators count calendar days, including leap years. The time duration calculator handles shifts that run past midnight. The unit converter covers length, weight, and temperature, and the GPA calculator weights each grade by credit hours.
Privacy
The arithmetic runs in your browser. Nothing you type into a calculator, whether a salary, a loan balance, or a date of birth, is sent to a server or stored.