Age Calculator

An age calculator is an online tool that calculates a person's age from their date of birth. It can show age as years, months and days and can also calculate age on a specific date instead of only using today's date.

A precise age calculation uses calendar dates rather than simply dividing the number of days by 365. This matters because months have different lengths and leap years add an extra day to February.

An age calculator can also provide useful information such as total days, weeks or months and the date of the next birthday.

Using an age calculator is simple. Enter your date of birth and select the date on which you want to calculate the age. By default, the reference date can be today's date.

1. Enter your date of birth.
2. Select the date for which you want to calculate the age.
3. Run the calculation.
4. Review the exact age in years, months and days.
5. Check additional results such as total days and the next birthday when available.

You can change the reference date to calculate how old someone was in the past or how old they will be on a future date.

Exact calendar age is calculated by comparing the year, month and day of birth with the reference date. The calculation accounts for the actual length of each calendar month and leap years.

For example, a person born on 15 March 2000 reaches 26 years on 15 March 2026. If the reference date is 30 May 2026, the calendar age is 26 years, 2 months and 15 days.

This calendar-based approach is more appropriate for displaying an age in years, months and days than simply converting a number of elapsed days into years.

Years, months and days provide the most familiar way to describe a person's calendar age.

For example:

Date of birth: 15 March 2000
Reference date: 30 May 2026
Age: 26 years, 2 months and 15 days

The result is based on the calendar relationship between the two dates. It should not be interpreted as simply converting a fixed number of days into a fixed number of months or years because calendar months have different lengths.

You can calculate age on a date other than today by entering a custom reference date. This is useful when checking someone's age on a past or future date.

For example, if someone was born on 10 August 2005, you can calculate their age on 1 January 2025 by using 1 January 2025 as the reference date.

The same method can be used for future dates. The calculator compares the date of birth with the selected reference date and returns the calendar age for that date.

In addition to calendar age, an age calculator can show elapsed time in units such as days, weeks and months.

Total days represent the number of calendar days between the date of birth and the reference date. Total weeks can be calculated from elapsed days, while total months can be expressed using a defined calendar-month calculation.

These values are useful when you need a different representation of age, but they should not be confused with the calendar result of years, months and days.

For example, 1 year is not always exactly 365 days because leap years contain 366 days.

Leap years are important when calculating elapsed time because a leap year contains 366 days instead of 365. February has 29 days during a leap year and 28 days during a common year.

A person born on February 29 has a birthday date that does not occur in every calendar year. Different applications and jurisdictions can use different conventions when determining the birthday date in a non-leap year.

For this reason, an age calculator should clearly define how February 29 birthdays are handled rather than assuming that every system follows the same convention.

To find the next birthday, compare the month and day of the birth date with the current date. If the birthday has already occurred this year, the next birthday falls in the following year.

An age calculator can show the date of the next birthday and the number of days remaining until that date.

For birthdays on February 29, the next-birthday result depends on the convention used for non-leap years. A calculator should make that behavior clear when this date is entered.

Here are some simple examples of calendar age calculations:

• 15 March 2000 to 30 May 2026: 26 years, 2 months and 15 days.
• 1 January 2010 to 1 January 2026: 16 years exactly.
• 10 August 2005 to 10 August 2025: 20 years exactly.
• 1 June 2020 to 15 June 2026: 6 years and 14 days.

These examples demonstrate why the exact result depends on the relationship between the two calendar dates rather than only on the number of years between them.

An age calculator can provide an exact calendar result when the date of birth, reference date and calculation rules are correct. The result in years, months and days is based on the calendar dates entered by the user.

Differences between age calculators can occur when they use different rules for time zones, February 29 birthdays, date formats or the definition of elapsed months and days.

For official applications, legal eligibility or institutional requirements, use the date and age rules specified by the relevant organization or authority.