Age Calculator

Calculate age from a birth date

Enter a date of birth and a reference date to see full age, Japanese counting age, and the number of days until the next birthday.

How to use

1. Enter the date of birth.
2. The reference date is filled with today by default and can be changed.
3. Select Calculate to view the age and next birthday information.

Full age and Japanese counting age

Full age starts at 0 at birth and increases at the end of the day before each birthday. Because this tool calculates by calendar date, it shows the new full age on the birthday itself. Japanese counting age starts at 1 at birth and increases every January 1.

Next birthday

When the reference date is the birthday itself, that date is shown and the remaining days are 0. For February 29 birthdays, February 28 is used in non-leap years.

FAQ

How is full age calculated?

Full age starts at 0 at birth. A person turns 1 at the end of the day before their first birthday, and the age increases the same way each year. Because this tool calculates by calendar date, it shows the new full age on the birthday itself.

How is Japanese counting age calculated?

Japanese counting age starts at 1 at birth and increases every January 1. It is calculated as the reference year minus the birth year plus 1, regardless of whether the birthday has occurred.

Can I change the reference date?

Yes. You can calculate age as of a past or future date.

What happens when the reference date is blank?

Today is filled automatically using the device’s local date.

How is February 29 handled?

In non-leap years, February 28 is used as the birthday.

Is my date sent to a server?

No. Date parsing and calculation are performed entirely in your browser.