Couple D-Day Calculator
Couple milestones like 100 days and anniversaries.
Left blank, today's date is used.
Days together
0 days
Enter the day you started dating.
| Milestone | Date | D-day |
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What is a couple anniversary D-day?
This calculator shows how many days you've been together since your start date, and how far away milestones like the 100th day or your 1-year anniversary are. Enter just the start date to see the days-together count and a list of upcoming anniversaries.
How it is calculated
Days together = (reference date − start date) + 1, counting the start date itself as day 1. The date difference is computed at UTC midnight to avoid off-by-one errors from daylight saving time or timezone shifts.
Day-count milestones (100, 200, 300, 500, 1000, 2000) fall on the start date plus (N − 1) days. Year anniversaries (1, 2, 3, 10 years) fall on the same month and day each year; if the start date is Feb 29, non-leap years use the last day of February instead.
Real-world uses
Use it to check how long you've been dating, plan ahead for an upcoming 100th day or anniversary, or compare past and upcoming milestones at a glance.
Settling how you count together
Couple anniversaries have no legal definition, so the rule is whatever the two agree on — but if the counting is never settled, the dates drift apart by a day and each ends up marking a different one.
Whether day one is the first day
The common Korean convention counts the day you met as day one, putting the hundredth day 99 days later.
Starting the count the next day pushes it back by one. Either works, but it is easier to fix the rule once — calculators and apps default differently, and two people can end up looking at different dates.
Year marks and day marks
Day-count marks (100, 200, 1000) and calendar marks (first, second year) are computed differently — a thousandth day lands around two years and nine months, not on the third anniversary.
A first anniversary is the same calendar date the following year; a leap year makes the elapsed count 366 days while the date stays the same.
For a 29 February start, simply agree in advance on 28 February or 1 March for common years.
Legal basis
- General rules on periods — Civil Act arts. 155–161 (not binding on customary anniversary counting)