How to read D-day notation
- D-30: 30 days left until the target date.
- D-day: today is the day.
- D+30: 30 days have passed since the target date.
Why count the start date as day 1?
In Korea, a couple’s 100th day or a baby’s 100th day (baek-il) is usually counted with the day you met (or were born) as day 1. So the 100th day falls 99 days after the start date. When counting “how many days have passed”, on the other hand, the start date is usually day 0, so choose the rule that fits the situation.
Start date = day 0: the Nth day = start date + N days
Yearly anniversaries such as the 1st or 2nd anniversary fall on the same calendar date (e.g. 14 March → 14 March the next year) regardless of this rule.
Example
Counting the start date as day 1, the 100th day is Friday 10 April 2026, the 200th day is Sunday 19 July, and the 1st anniversary is Friday 1 January 2027.
Counting the start date as day 0, the 100th day is one day later, Saturday 11 April. The same milestone can differ by a day depending on the rule, so agree on it in advance.
Common uses for anniversary counting
- Couples: 100 days, 200 days, 300 days, the 1st anniversary and 1,000 days
- Babies: baek-il (the 100th day including the birthday) and the first birthday (dol)
- Goals: checking how many days since you quit smoking or started exercising
- Military service: days since enlistment and days left until discharge
Frequently asked questions
How is a baby’s 100th day (baek-il) calculated?
Count the birthday as day 1 and add 99 days. In the anniversary calculator above, choose “Start date = day 1” and enter the birthday.
How do you count D-day for an exam?
The exam day is D-day and the day before is D-1. Enter the exam date as the target date to see the days left from today.