What is an age calculator?

An age calculator works out the exact time that has passed between a date of birth and another date, usually today. Instead of just giving a number of years, it breaks the result into completed years, months and days. This is useful for forms, school and sports registrations, insurance, retirement planning, medical records, pet care, and for simple curiosity about how many days you have been alive.

How this age calculator works

The calculator compares the two dates in three steps:

1. Subtract the birth year from the current year, the birth month from the current month, and the birth day from the current day.
2. If the day difference is negative, borrow the number of days in the previous month and reduce the month count by one.
3. If the month difference is negative, borrow 12 months and reduce the year count by one.

The total number of days is found by counting the real calendar days between the two dates, so leap years are included correctly. Weeks, hours and months are then worked out from those totals. All calculations use calendar dates, so your time zone does not change the result.

How to use the calculator

1. Pick your date of birth using the date box. On a phone, the built-in date picker opens.
2. Leave the second date as today, or choose another day to find an age on a past or future date.
3. The result updates when you press Calculate or change a date.
4. Scroll down to see your birthday countdown and milestone dates.

Worked example

Imagine someone was born on May 15, 1990 and we calculate their age on November 4, 2026. Years: 2026 − 1990 = 36. Months: 11 − 5 = 6. Days: 4 − 15 = −11, which is negative. So we borrow the 31 days of October, which gives 20 days, and reduce the months to 5. The age is 36 years, 5 months and 20 days.

In total that is 437 months, or 13,322 days (1,903 weeks and 1 day), or 319,728 hours. The person was born on a Tuesday, and the next birthday on May 15, 2027 is 192 days away.

Leap years and February 29 birthdays

A normal year has 365 days, but about every four years a leap year adds a 29th day to February. In the Gregorian calendar, a year is a leap year if it is divisible by 4, except for century years, which must be divisible by 400. That is why 2000 was a leap year, while 1900 was not. This calculator counts those extra days automatically.

People born on February 29 are sometimes called "leaplings". In years that are not leap years, they celebrate on February 28 or March 1 depending on personal preference, local customs and the law. This calculator uses February 28 as the birthday in non-leap years.

Why exact age matters

• School and sports: many programs use an age cut-off date to decide which class or team a child joins.
• Insurance and pensions: prices and eligibility often depend on age on a specific date.
• Legal ages: driving, voting, working and other rights begin at certain ages.
• Healthcare: doses, screenings and growth charts depend on exact age, especially for babies and children.
• Planning: retirement, anniversaries and milestone birthdays.

Different ways of counting age around the world

Most countries count age as the number of birthdays you have completed, which is what this calculator shows. Traditionally, Korea and some other East Asian countries counted a person as one year old at birth and added a year on New Year’s Day. South Korea changed its legal and administrative age to the international system in June 2023, so official documents now use the same method as this calculator. If you need a traditional age for a cultural reason, add one year to the number of years the calculator gives you and check whether the person has had their New Year’s Day yet.

About the milestone table

The milestone table lists the dates when you turn important ages, such as 18, 21, 30, 40, 50, 60 and 65, and the dates when you reach 5,000, 10,000, 15,000, 20,000, 25,000 and 30,000 days old. Each row tells you whether the date has already happened or how many days remain. Day milestones are a fun way to celebrate: someone born on May 15, 1990 reached 10,000 days old on September 30, 2017.

Frequently asked questions

How do I calculate my age in years, months and days?

Subtract your birth date from the current date, borrowing days from the previous month and months from the previous year when needed. This calculator does that for you instantly.

How many days old am I?

The calculator shows the total number of calendar days between your birth date and the chosen date, including all leap days.

Can I find my age on a past or future date?

Yes. Change the second date to any day after your date of birth. This is helpful for forms that ask for your age on a specific cut-off date.

Does the calculator include the time of day I was born?

No. It works with calendar dates only, so the hours shown are the number of full days multiplied by 24.

Is my information stored?

No. Everything is calculated in your browser, and your date of birth is never sent to our servers or saved.

Helpful resources

• Uses for the Date Calculators (timeanddate.com): examples of calculating durations and ages between dates.
• Leap year (Encyclopaedia Britannica): how leap years work in the Gregorian calendar.
• What years are leap years? (National Research Council Canada): the three leap year rules explained.
• Percentage Calculator on this site: handy for everyday percentage questions.

This calculator is for general information only. For legal or medical purposes, always confirm dates using official documents. See our Terms & Disclaimer.