“How old am I exactly right now?” “I need to write my age on a form.” When you need an exact age, the calculation rules can be confusing.
In this article, we explain how to calculate your exact age, including how birthdays and leap-day (February 29) births are handled, with concrete examples.
What is “exact age”?
In Japan, “age” generally means exact age (満年齢). Under Japanese law (Act on Calculation of Age), the rules are:
- Age starts at 0 on the day of birth
- One year is added on each birthday
In other words, your age is how many years have passed since your birth. You are 0 at birth and turn 1 on your first birthday.
Note: The traditional "counted age" (数え年) counted the birth year as age 1, but modern law and daily life use exact age.
How to calculate exact age
Follow these three steps:
Subtract the birth year from this year
Example: 2026 - born in 1990 = 36
Check whether this year's birthday has passed
If today is your birthday or later, the number from step 1 is your age.
Subtract 1 if it hasn't
If your birthday hasn't arrived yet, subtract 1 from the step 1 number.
Examples
| Date of birth | Age as of today (August 11, 2026) |
|---|---|
| March 15, 1990 | 36 (birthday has passed) |
| October 1, 1990 | 35 (birthday hasn’t arrived: 36-1) |
| August 11, 2026 | 0 (on the birth date itself, age is 0) |
What age do you turn on your birthday?
On your birthday itself, you turn the new age. Someone born on March 15, 1990 turns 36 on March 15, 2026. They are 35 until the day before, and 36 from the birthday onward.
Legally, the age increments at the end of the day before the birthday, but in practice the birthday itself is treated as the new age.
What about February 29 births?
For people born on February 29, February 28 is treated as the birthday in non-leap years. This is stipulated by the Act on Calculation of Age.
- Leap years (when February 29 exists): increments on February 29
- Other years: increments on February 28
Key point: If you were born on February 29, check whether your age increments on February 28 or 29 in the current year.
Calculate your age easily
Manual calculation works, but handling leap years and birthday timing correctly is surprisingly fiddly.
The Tools Hub age calculator automatically computes your exact age as of today and the days until your next birthday.
Enter your birth date
Pick your date of birth from the calendar.
Automatic calculation
Your exact age as of today is shown. February 29 births are handled correctly automatically.
Check your next birthday
See how many days until your next birthday and the age you will turn.
Tool mentioned in this article
Age Calculator
Enter your birth date to get your exact age as of today and the days until your next birthday.
Summary
- Exact age adds one year on each birthday
- You turn the new age on your birthday itself
- February 29 births use February 28 in non-leap years
- The Tools Hub age calculator handles leap years correctly for you
When you need an exact age for forms or verification, refer to the rules in this article - or just use the calculator.
FAQ
What is the difference between counted age and exact age?
Counted age counts the birth year as age 1; exact age adds one year per birthday. Modern law and daily life use exact age.
Do I turn the new age on the birthday or the day before?
Legally the age increments at the end of the day before the birthday, but in practice the birthday itself is treated as the new age.
When is the birthday for February 29 births?
February 29 in leap years, February 28 in non-leap years.