Korean 100-day calculator

Add 100 days to the date you started and you will be one day late. This trips up almost everyone doing it in their head.

Korea counts the starting day as day one. The day you met is not day zero, it is already day 1. So day 100 is 99 days later, and adding a full 100 lands you on day 101.

The same rule runs through everything counted in days here — a couple’s 100th day, a baby’s 100th day, hospital day counts. If a Korean friend gives you a date that is one off from yours, this is why.

Baek-il literally means “hundred days”. It is marked with a small party and a photo shoot, and it matters more than a Western family might expect.

The reason is historical. Infant mortality was high enough that surviving the first hundred days was the real milestone — so the celebration is for having got there, not for the number itself.

What people actually do: a table setting (백일상) with rice cakes and fruit, a professional or home photo shoot, and close family only. It is much smaller than the first birthday.

Dol is the first birthday and it is the big one. Traditionally a large party with extended family, a dedicated outfit, and a table of food and rice cakes.

The part visitors remember is doljabi (돌잡이): the baby is offered objects and whichever they grab is read as a hint about their future. Thread for a long life, money for wealth, a pencil for scholarship.

Note that dol is counted by date, not by days. Born on 20 October, the dol is 20 October the following year. In day counting that is day 366, which looks wrong next to “365 days” but is not — a year of dates and a count of days are two different things.

Many families hold the party on the weekend before, since a weekday dol is hard for relatives. The table above shows which weekday it falls on so you can plan around it.

Korean couples celebrate 100 days, 200 days, 300 days and 1,000 days as much as they celebrate years. The 100th day is the one everybody knows.

A thousand days lands about two years and nine months in — sooner than people expect. 500 days arrives roughly four months after the first anniversary.

Anniversaries by year work like dol: you match the date, not the day count. Which is why the day column beside a one-year mark reads 366 rather than 365.

Count from the start date itself. Adding the round number to your calendar is the single most common mistake.

A leap day shifts the day count, not the date. If 29 February falls inside the year, a one-year mark reads day 367 instead of 366. The date is still the date.

Born on 29 February? There is no such date in ordinary years. This calculator rolls forward to 1 March; some families pull back to 28 February instead. Pick one and stay with it.

Working out ages in Korean counting instead? That is a separate system — the Korean age calculator lays out all three.