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Date Calculator (D-Day)

Count the days to a date or since one, and add or subtract days, weeks, months and years.

Count the days

Days to go, days since, or the date a set period from now.

What are we working out?

Days left until the date you enter (D-), or days since it (D+).

Dates and counting
YYYY/MM/DD

Defaults to today. Change it to count from another day.

YYYY/MM/DD

A future date gives D-, a past date gives D+.

Counting

The day itself is day zero

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How the counting works

SettingThe day itselfOne day later
Skip todayD-DAYD+1
Count todayDay 1Day 2

Two conventions sit one day apart. Pick the one that matches what you are counting.

Learn more 📚

Reading D-Day notation

What you seeWhat it means
D-30Thirty days to go
D-1Tomorrow
D-DAYToday is the day
D+1One day has passed
D+100A hundred days have passed

The notation came from military planning and stuck. In Korea you will see it on exam countdowns, discharge dates, product launches and couple apps.

Two ways to count, one day apart

SettingThe day itself isUse it for
Skip todayDay zero, written D-DAYExams, interviews, filing deadlines
Count todayDay oneAnniversaries, a baby's age in days, couple counts

This is why two countdown apps can disagree by a day on the same date. Pick the setting that matches what you are counting rather than assuming one is wrong.

The milestones Korea counts

MilestoneLands onWhy people mark it
Day 10099 days after the start dateThe best known couple milestone, and also a baby's first celebration
Day 200, Day 300199 and 299 days afterKept up between the bigger dates
Day 1000999 days afterTreated as the serious one, roughly two years and nine months
AnniversariesThe same calendar date each yearCounted by date, not by day count

Day counting starts at 1 on the day itself, so Day 100 is 99 days later, not 100. Enter a past date and this calculator lists the next five milestones with the date each one falls on.

Adding months, and the end of the month

You ask forYou getWhy
January 31 plus 1 monthFebruary 28February has no 31st
January 31 plus 1 month, leap yearFebruary 29The rule takes the last day that exists
March 31 plus 1 monthApril 30April has 30 days

Adding a month keeps the same date number when that date exists, and otherwise falls back to the last day of the target month. This is how Korean law counts periods, and the result is flagged when it happens.

Adding days and weeks has no such trap. Seven weeks is always 49 days, whatever month you land in.

FAQ ❓

D minus a number is how many days are left, so D-30 is thirty days to go and D-1 is tomorrow. D-DAY is the day itself. D plus a number is how many days have passed. The notation came out of military planning and is used all over Korea for exam countdowns, discharge dates and product launches.
Because they use different conventions for the day itself. Deadlines treat today as day zero, while anniversaries and baby day counts treat it as day one. Neither is wrong, so pick the setting that matches what you are counting.
Ninety-nine days after the start date, because the start date itself is day one. This is the milestone Korean couples mark, and it is also a baby's first celebration. The calculator lists Day 100, 200, 300, 500 and 1000 along with yearly anniversaries.
Day counts give you something to mark long before a first anniversary comes around. A hundred days is close enough to feel soon, a thousand days sits at about two years and nine months, and both are widely celebrated.
You get February 28, or February 29 in a leap year. Adding a month keeps the same date number when that date exists and otherwise falls back to the last day of the target month. Korean law counts periods the same way, and the result flags it when it happens.
No. Everything runs in your browser, nothing is sent anywhere, and there is no sign-up. A share link carries the dates in the address itself, so it only exists if you create one.

Sources 🌐