Everyone in Japan could have the same surname by 2531 due to unique law

A new study has projected everyone in Japan will have the same surname by 2531 and people thought it was an April Fool’s prank.

In Japan, married couples are legally obliged to have the same family name in a law that dates back to the civil code implemented in the late 1800s.

But according to a study by Hiroshi Yoshida, a professor of economy at Tohoku University's Research Center for Aged Economy and Society, it is projected that every person in Japan will have the surname “Sato-san” in just over 500 years’ time unless the law changes to allow married couples to have separate surnames if they want to.

Yoshida explains that the study relies on several assumptions, but that it paints an interesting picture about the future of Japanese society that will help draw attention to it.

He explained to Mainichi Japan: “If everyone becomes Sato, we may have to be addressed by our first names or by numbers. I don't think we can call that a good world to live in.”

Currently, Sato is the most popular surname in Japan, with 1.529 per cent of the population bearing that family name.

Yoshida used calculations, including the proportion of the population with the surname Sato and the estimated growth rate, to project how the single surname system may affect the diversity of names.

He concluded that over half of the population will have the surname Sato by 2446. By 2531, everyone will have that surname.

However, a 2022 survey found that, 39.3 per cent of single people said they would want to have the same surname as their husband or wife, even if the selective separate surname system was introduced. Using this figure, Yoshida predicted that everyone would have the Sato surname by 3310.

Currently, Japan is the only country in the world that legally requires married couples to use the same surname.

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