Age Calculator

How age is calculated, and why answers differ

Working out an age sounds trivial until you try it across month boundaries and leap years. This page explains the method used here, the places where other calculators disagree, and how to get an answer a form will accept.

The calendar method

This calculator uses the method almost every official form assumes. It subtracts the birth year from the reference year, then adjusts if the birthday has not yet happened that year. Months and days are then filled in by borrowing from the previous month, the same way you would do a subtraction by hand. Someone born on 20 March 1994, measured on 5 September 2026, is 32 years, 5 months and 16 days old.

Because the number of days in a month varies, the "borrowed" value depends on which month you borrow from. Borrowing from February gives 28 days, or 29 in a leap year, while borrowing from July gives 31. That is why two calculators can produce slightly different day counts, and why the years and months figure is the one to trust for paperwork.

Using the calculator

1. 1Enter the date of birth. The field uses your device date picker, so the format matches your region automatically.
2. 2Leave the second date as today, or set it to a future or past date - useful for eligibility cut-offs and school admission dates.
3. 3Read the exact age, then the supporting figures: total days, total weeks and months, birth weekday and the countdown to the next birthday.

What each result is good for

• Years, months and days is the format visa applications, insurance forms and school registrations expect.
• Total days lived is the figure people use for milestone celebrations - the 10,000th day arrives just after the 27th birthday.
• Birth weekday answers the "what day was I born on" question without a perpetual calendar.
• Next birthday countdown is handy when you are planning around a legal age threshold rather than a party.

Leap years, and the 29 February problem

A leap year adds a day roughly every four years to keep the calendar aligned with the solar year of about 365.2422 days. The rule is more precise than most people remember: a year is a leap year if it is divisible by four, unless it is divisible by 100, unless it is also divisible by 400. So 1900 was not a leap year, but 2000 was.

People born on 29 February have no birthday in most years. Jurisdictions differ on whether they legally age on 28 February or 1 March, which affects things like driving licences and drinking ages. This calculator treats the anniversary as 1 March in non-leap years, which matches the more common legal convention, but it is worth checking local rules if the exact day matters.

Different ways of counting age

The Western convention starts everyone at zero and adds a year on each birthday. It is not the only system in use. Traditional East Asian age reckoning counts a newborn as one year old and adds a year at the new year rather than on the birthday, which can put someone up to two years ahead of their international age. South Korea moved to the international system for most official purposes in 2023, but the older count still appears in conversation.

Insurance companies add their own twist with "age nearest birthday", which rounds to whichever birthday is closer. That can quietly change a premium band, which is a good reason to check exactly how a provider defines age before you compare quotes.

Common uses for an exact age

School admissions usually set a cut-off date and ask for the age on that specific day, which is exactly what the reference-date field is for. Sports leagues often work from age on 1 January or 1 September. Retirement and pension calculations need the precise date a threshold is crossed. In every one of these cases, an approximate age is not good enough and a quick check avoids a rejected application.

Related tools

If you need to express an age difference as a proportion, the Percentage Calculator will do it in one step. The BMI Calculator often asks for an age alongside height and weight, and the Unit Converter is useful when a form wants measurements in units you do not normally use.