How D-day is calculated
D-day is the target date minus today. If the target is still ahead it's shown as D-, if it has passed it's D+, and D-DAY marks the day itself.
More detail
Reading D-day notation
D-100 means the target date is 100 days away; D+100 means it was 100 days ago. It's the standard way to count down to an exam or wedding, or count up from an anniversary.
Tip. Use the day count for anniversaries (how many days you've been together), and the D-day value for countdowns to a future date like an exam or trip.
Frequently asked questions
What's the difference between D-day, D-, and D+?
D-100 means the target date is 100 days away, D-DAY is the day itself, and D+100 means it was 100 days ago. This calculator switches automatically based on today's date.
How is D-day calculated?
D-day = target date − today. Enter any future or past date and the calculator shows both the D-day label and the exact number of days remaining or elapsed.
How do I count '며칠째' (day count) for an anniversary?
For a past or today's target date, the Day count output adds 1 to the elapsed days, so the day you met counts as day 1 rather than day 0.
Can I use this for a future exam or trip countdown?
Yes — enter the future date as the target. The D-day output counts down (e.g. D-30), and Days left shows the exact number of days remaining.