When Did People in Japan Grow Older?

The Curious Story of Birthdays and Kazoedoshi

“Your birthday is the day you turn a year older.”

For us today, this seems completely natural.

Someone born on December 31 turns one on the following December 31. Someone born on January 1 turns one on the following January 1.

But in Japan, people once counted their age differently.

For centuries, a traditional system called kazoedoshi was widely used.

Under this system, a baby was considered one year old at birth. Then, everyone became one year older at the beginning of the new year.

In other words, your birthday was not necessarily the day you gained a year of age. The beginning of a new year was.

So what did birthdays mean to people in the past?

Everyone Grew One Year Older Together

Under the kazoedoshi system, a newborn was counted as one year old from the moment of birth.

Then, when New Year’s Day arrived, the child became two years old.

For us today, that may sound rather strange.

But it was not simply an old-fashioned way of counting incorrectly.

According to the National Astronomical Observatory of Japan, the traditional Japanese lunisolar calendar had a different structure from the modern Gregorian calendar. Because the length of months and years was not as straightforward as it is today, counting age from one’s birthday was not always convenient.

Kazoedoshi offered a simple way to count age: one year at birth, followed by another year at each New Year.

This meant that, in traditional Japan, people often thought of age in terms of the changing year rather than the individual birthday.

A new year meant that everyone had grown one year older.

New Year’s Day was therefore not only the beginning of a new calendar year. It was also a milestone in people’s lives.

Did People in the Past Not Have Birthdays?

At this point, it would be easy to assume that birthdays did not exist in traditional Japan.

But that would be misleading.

Birthdays were celebrated in Japan long before the modern system of age calculation became standard.

Research by Yumi Uzawa on birthdays in early modern Japan shows that birthday celebrations existed during the Edo period.

They were not limited to the shogun, daimyo, and members of the aristocracy. Examples have also been found among lower-ranking samurai and ordinary people.

Families might celebrate a child’s or grandchild’s birthday by preparing sekihan, a traditional red-bean rice dish, and sharing food with relatives and neighbors.

So birthdays were certainly meaningful.

The important distinction is this:

A birthday could be a special day without being the day when a person officially became one year older.

That distinction is easy to miss when looking at the past through modern eyes.

Your Birthday and Your Age Were Two Different Things

Imagine a child whose birthday was in December.

Under the kazoedoshi system, the child did not necessarily become a year older on that December birthday.

Instead, when the New Year arrived, the child—and everyone else—gained another year.

The family might still celebrate the child’s birthday.

But the birthday and the annual increase in age were separate things.

This gives New Year’s Day a very different meaning from the one we usually give it today.

People welcomed the new year, celebrated with their families, prayed for good fortune, and prepared special foods.

At the same time, they entered another year of their lives.

For people living under this system, the New Year was something like a shared birthday for everyone.

That is quite different from our modern experience, in which each person has an individual day on which they grow older.

Birthdays Were Still Important to Children

If birthdays did not determine age, why celebrate them?

Research on Edo-period birthday customs suggests that birthday celebrations were particularly meaningful within families, especially for children and grandchildren.

Families prepared special foods, offered them to the gods, and sometimes invited relatives and neighbors to share a meal.

Red rice, rice cakes, sake, and other foods could be part of these celebrations.

These customs were not simply about marking the number of years someone had lived.

They could also express gratitude that a child had safely reached another stage of life, along with hopes for continued health and happiness.

In that sense, the meaning of a traditional Japanese birthday may have been closer to celebrating a person’s continued life and growth than to simply announcing a new age.

When Did Japan Begin Using the Modern Age System?

So when did the modern idea of “turning a year older on your birthday” become established in Japan?

One important turning point came during the Meiji period.

In 1902, Japan enacted the Age Calculation Act.

The law stated that age was to be calculated from the date of birth.

This established a legal basis for calculating age from a person’s birth date.

However, this did not mean that everyone in Japan immediately stopped using kazoedoshi in everyday life.

There was a difference between how age was legally calculated and how people commonly expressed their age.

The traditional system continued to be used in everyday life for some time.

From Kazoedoshi to Full Age

Another important change came after World War II.

In 1949, Japan enacted the Act on the Manner of Stating Age.

The law encouraged people to stop expressing their age using kazoedoshi and instead use the age calculated under the 1902 Age Calculation Act.

It also required national and local government bodies to use this method when stating people’s ages.

The law came into effect on January 1, 1950.

So the transition from kazoedoshi to the modern system was not an overnight change in 1902.

Rather, the legal system changed first, while traditional ways of thinking and speaking about age continued in everyday life.

Eventually, the modern system became the norm.

And today, we naturally think:

Birthday → another year older.

And Then There Is “Hayaumare”

Even today, Japan has an interesting connection between age, the calendar, and social systems.

One example is hayaumare, a term used for children born early in the calendar year.

Japan’s school year begins on April 1 and ends on March 31 of the following year. Children born between April 2 of one year and April 1 of the following year generally enter elementary school in the same school year.

Why is April 1 treated differently?

Under Japan’s Age Calculation Act, a person reaches the next age at the end of the day before their birthday. This means that a child born on April 1 reaches the required school age at the end of March 31 and enters elementary school on April 1.

As a result, an April 1-born child is grouped with children born from April 2 of the previous year, rather than with children born after April 1 of the same year.

It is a small reminder that even today, age, the calendar, and social institutions do not always line up as neatly as we might expect.

From a Shared New Year to a Personal New Year

In traditional Japan, kazoedoshi meant that many people effectively grew older together at the beginning of the new year.

Today, each person grows older on their own birthday.

Birthdays themselves have not disappeared from the story. In fact, they have become even more closely connected with our individual sense of age.

But the relationship between birthdays and age has changed.

In the past, people grew older together.
Today, each of us grows older on our own birthday.

Age may seem like a simple number telling us how long we have been alive.

But the history of age tells us something else.

Age is also shaped by calendars, laws, schools, customs, and the way a society divides up time.

And when we look at the past through that lens, New Year’s Day takes on a different meaning.

For people who used kazoedoshi, the arrival of a new year was not simply the turning of a calendar page.

It was also the moment when everyone moved one year forward in life.

The year changed.
The season changed.
And people grew one year older.

Perhaps that is one reason the arrival of a new year once felt so deeply connected with the passage of human life.

Sources and Further Reading

• National Astronomical Observatory of Japan, Koyomi Wiki: Age. Information on kazoedoshi and the differences between traditional and modern age calculation.
• National Diet Library, Age Calculation Act (年齢計算ニ関スル法律), enacted in 1902.
• House of Representatives of Japan, Act on the Manner of Stating Age (年齢のとなえ方に関する法律).
• Yumi Uzawa, “Birthdays in Early Modern Japan: From the Shogun to Commoners,” Bulletin of the National Museum of Japanese History, No. 141, 2008.
• Ministry of Education, Culture, Sports, Science and Technology, When Does a Child Born on April 1 Enter Elementary School?