Calculators
Calculations by the official rules of each country, with the sources shown. What you enter is processed in your browser.
Money & percentages
Percentage Calculator
Work out a percentage of a number, what percent one number is of another, the percent change between two numbers, and prices before or after a discount or markup.
VAT Calculator
Add VAT to a net price or take it out of a gross price with the current rates of the UK and 15 other countries, for one amount or a whole invoice, with the rounding your invoices use.
Loan Calculator
Work out the monthly payment, total interest and full repayment schedule of a loan or mortgage, with equal payments, equal principal or interest only, and an optional interest-only period.
Compound Interest Calculator
See how savings or an investment grow with compound interest: a starting amount, regular contributions, any compounding frequency, and a year-by-year table, compared with simple interest.
Health
BMI Calculator
Calculate your body mass index in metric or imperial units and see your weight class under the WHO standard or the national standard of Korea, Japan, China, the UK, Indonesia or Thailand, with the healthy weight range for your height.
Calorie Calculator
Estimate your basal metabolic rate and the calories you need a day at your activity level, with the Mifflin-St Jeor or Harris-Benedict equation, the FAO/WHO/UNU equations, or Japan's and Korea's dietary reference intakes.
Age
Age Calculator
Find your exact age from your date of birth, or the age on any date: years, months and days, total months, weeks and days, the day you were born and the countdown to your next birthday.
Korean Age Calculator
Work out an age the ways Korea counts it: international age, used by law since 28 June 2023, year age and the traditional counting age, with the days to the next birthday and lunar birthdays.
Choosing the right calculator
The Percentage Calculator answers the everyday questions: a percent of a number, the percent change between two values and the price before or after a discount, worked out exactly. The Loan Calculator gives the monthly payment, total interest and a full schedule for equal payments, equal principal, interest only or a flat rate, and the Compound Interest Calculator shows how savings grow with regular deposits and any compounding frequency.
The VAT calculator adds VAT to a net amount or takes it out of a gross one, for a single amount or an invoice with several lines. It picks the rate by the date of the sale from the checked rates of 16 countries, including the UK, the main EU countries, Japan, Korea and China, and rounds per line or once per rate, as you choose.
The BMI Calculator and the Calorie Calculator let you choose the standard instead of the page language choosing it for you: the WHO and US CDC classes, the UK NICE thresholds, or the national cut-offs of Korea, Japan, China, Indonesia and Thailand for BMI, and Mifflin-St Jeor, Harris-Benedict, FAO/WHO/UNU or the 2025 dietary reference intakes of Japan and Korea for calories.
The Age Calculator gives an exact age in years, months and days on any date, with the days lived and the next birthday; you choose how 29 February birthdays count, and it can show the day Japanese law treats an age as reached.
The Korean Age Calculator works out an age the three ways Korea counts it: international age (만 나이), which the Civil Act and the Framework Act on Public Administration have used since 28 June 2023, year age, still used by laws such as the Juvenile Protection Act and the Military Service Act, and the traditional counting age. It shows the days to the next birthday, handles 29 February birthdays by the Civil Act period rules and accepts a lunar birthday, converted with the Korean (KASI) lunar calendar.
These calculators run in your browser, and the amounts and dates you enter are not sent to LeedyBox or saved. Each tool page names the official sources of its rules and the date they were last checked.