South Koreans are set to become one or even two years younger - at least on official paperwork.
On Thursday, the South Korean parliament passed a law to scrap Korea's two traditional methods of counting age.
From June 2023, the so-called "Korean Age" system will no longer be permitted on official documents.
Only the standardised, internationally recognised method will remain.
The government is fulfilling a campaign promise to reduce confusion by adopting the same system used in the rest of the world.
Currently, the most widely used calculation method in Korea is the so-called "Korean age system", in which a person is one year old at birth and then gains a year on the first day of each new year.
In a separate method - the "counting age" - a person's age is calculated from zero at birth and a year is added on 1 January. This method exists primarily to calculate the legal age to drink alcohol and smoke.
But South Korea also uses the globally recognised system in which age is calculated by an individual's birthday and the first birthday is celebrated 365 days after birth.
This means that, for example, as of 8 December 2022, a person born on December 31 2002 is 19 under the international system, 20 under the counting system and 21 under the Korean system.
Yoo Sang-bum of the ruling People Power Party told parliament that "the revision is aimed at reducing unnecessary socio-economic costs, because legal and social disputes as well as confusion persist due to the different ways of calculating age".