How Age Is Counted in Japan: Western Age vs. Kazoedoshi (East Asian Age) and How to Build an Age Chart

Western age and kazoedoshi differ in where the count starts

Almost every age used in daily life in Japan is the Western-style age (man-nenrei): you are 0 on the day you’re born and gain a year on every birthday. With kazoedoshi, by contrast, you are already 1 at birth and gain a year every January 1. The only difference is whether the trigger is your birthday or New Year’s Day.

Kazoedoshi becomes easy to understand if you think of it as counting “how many New Years you have seen.” A child born on December 31 is already 2 on the next day, New Year’s Day. It looks extreme, but it simply counts calendar boundaries, and it isn’t wrong.

Legally, your age goes up the day before your birthday

Intuitively you get older on your birthday, but the legal treatment in Japan is slightly different. Under Japan’s Act on Age Calculation, the day of birth is the starting day, and following the rules for calculating periods, a year is added at the moment the day before your birthday ends. Someone born on April 1 gets a year older the instant March 31 ends.

• In everyday conversation, it’s fine to think you get older on your birthday; the difference only matters for official determinations
• People born on February 29 are treated as gaining a year when February 28 ends in common years, so they still age by exactly one year every year
• This day-before rule is the reason children born on April 1 are placed in the school year above in Japan
• Some systems, such as age conditions for insurance premiums or qualifications, are judged by the day-before rule

The kazoedoshi formula and how to build a quick chart

Kazoedoshi is simply the current year minus your birth year, plus 1. You don’t need to think about birthdays at all, so it is actually easier than Western age. In relation to Western age, it is Western age + 2 before your birthday that year, and Western age + 1 after it.

As the table shows, everyone’s kazoedoshi goes up together on New Year’s Day. That is exactly why shrines can post yakudoshi charts listed only by birth year. A Western-age chart, on the other hand, has to split into two columns depending on whether the birthday has passed.

Which count Shichi-Go-San, yakudoshi, and longevity celebrations use

Traditional events were all originally held by kazoedoshi. Today, however, more families use Western age, and practice varies by region, shrine, and temple. If in doubt, the surest way is to ask the shrine or temple you plan to visit, or your relatives.

The milestone celebrations are easier to remember once you know where their names come from. All of these are traditionally ages by kazoedoshi.

How to check both ages from a date of birth

1. 1

   Enter the date of birth

   Enter a date of birth in the “Find age” tab of the age calculator, and the Western age is shown as “X years, X months, X days.” Because months and days are shown as well as years, it also works when you need an age in months.

2. 2

   Change the reference date

   Enter the date you want to know about as the reference date, such as “April 1 this year” or “my start date at work.” It can be in the past or the future. The “Back to today” button restores the original state.

3. 3

   Check kazoedoshi at the same time

   The same screen lists kazoedoshi, the Chinese zodiac sign, the Western zodiac sign, the day of the week you were born, an approximate school grade, and the total number of days since birth. You get everything you need for paperwork in one place.

4. 4

   Copy and share the results

   The “Copy results” button copies everything at once, from the date of birth to the number of days until the next birthday. The dates you enter are only included in the share URL and are never sent to a server.

The part of Western age that trips people up when calculating by hand is the “X months, X days.” For people born at the end of a month, the number of days in a month varies from 28 to 31, which makes borrowing easy to get wrong. For documents where the number of days must be exact, using the calculated result as is is safer.

Common mistakes

• Confusing the calendar year with the fiscal or school year. In Japan, the fiscal year runs from April 1 to March 31 of the following year, three months off from the calendar year
• On a Japanese résumé, the age field normally shows your Western age as of the submission date or a specified reference date
• Almost no countries outside East Asia use kazoedoshi-style age. South Korea also officially standardized on Western age in June 2023
• Some systems judge conditions such as “age X or older” by the day-before rule, so you may qualify from the day before your birthday
• Because kazoedoshi increases on New Year’s Day, people born in December have the biggest gap from their Western age

You rarely have to think about kazoedoshi in daily life, but when you do, it’s almost always at a shrine, a temple, or a family occasion. To avoid panicking then, remember just one formula: subtract the birth year from the current year and add 1. That gets you through most situations. Yakudoshi and longevity celebrations are the typical times kazoedoshi is used; the age correspondences are listed in the yakudoshi age chart and the longevity celebration chart.

FAQ

How old am I in kazoedoshi?

Your kazoedoshi is the current year minus your birth year, plus 1. Someone born in 1996 is 2026 − 1996 + 1 = 31 in 2026. In relation to Western age, it is Western age + 2 before your birthday that year, and Western age + 1 after it.

Doesn’t your age go up on your birthday?

In everyday terms it does, but under Japanese law a year is added at the moment the day before your birthday ends. For someone born on April 1, that’s the end of March 31. You don’t need to worry about this in conversation, but the school-year cutoff and the age conditions of some systems in Japan are decided by this day-before rule.

Is Shichi-Go-San done by Western age or kazoedoshi?

Traditionally by kazoedoshi, but today many families use Western age, and most shrines say either is fine. To let siblings celebrate together, families sometimes use Western age for the older child and kazoedoshi for the younger one. If the shrine’s information specifies one, follow that.

Do people born on February 29 only age once every four years?

No, they gain a year every year. Because a year is added when the day before your birthday ends, in common years they are treated as gaining a year at the end of February 28. Whether to celebrate on February 28 or March 1 in non-leap years is just a matter of personal custom.