If you got together on January 1, 2026, day 100 is Friday, April 10
Korean couples usually count the day they got together as day 1. That makes day 100 the start date plus 99 days and day 1000 the start date plus 999 days. If you got together on Thursday, January 1, 2026, day 100 is Friday, April 10, day 200 is Sunday, July 19 and your first anniversary is Friday, January 1, 2027. Day 100 is a common milestone in Korean dating culture.
From one start date, the calculator above shows which day today is, how many years and months you have been together, and when the next anniversary falls and on which weekday. A timeline draws the stretch from the start date to the next major anniversary so you can see how far along you are, and you can pick dates to remember from the calendar and the list and save them to your calendar.
How to use the calculator
- Enter the start date: pick the first day you both count from. The day you decided to be a couple, the day you confessed or the day you met are all fine.
- Check how days are counted: by default the start date is day 1. Turn the switch off to count from day 0. Only the day milestones shift by one day; months and anniversaries stay the same.
- Read the result: the big number is which day today is, and below it are the time together and the next two anniversaries. Select a dot on the timeline, or move to it with the keyboard, to see that anniversary's date and the time left.
- List and calendar: the upcoming list can be viewed as all, days, months and years, or special dates. Select a date in the calendar and the box below shows which day it is.
- Save and share: choose from copying the result, copying a link (it reopens with the same start date) and saving a calendar (.ics) file. The date you enter is not sent to a server.
How the dates are calculated
| What you get | Calculation | Example, start 2026-01-01 |
|---|---|---|
| Which day today is | today - start + 1 | 2026-09-24 is day 267 |
| Day N | start + (N - 1) days | Day 100 = 2026-04-10 (Fri) |
| Month N | the same date N months later, or the last day of that month | Month 3 = 2026-04-01 |
| Anniversary N | the same month and day N years later, or February 28 | 1st anniversary = 2027-01-01 (Fri) |
| Time together | days elapsed, split into calendar years, months and days, and into weeks | 2026-09-24 is 8 months 23 days, 38 weeks 0 days |
The time together is counted in days that have elapsed from the start date to today. So on day 267 the time together is 266 days, which is 8 months 23 days. Months and anniversaries are always counted again from the start date, so a month that was moved to February 28 after a January 31 start comes back to March 31 the next month.
Quick check by start date
These dates are worked out in advance for start dates that couples often pick, such as Christmas, New Year and Valentine's Day. Other dates come out in the same format when you enter them in the calculator above.
| Start date | Day 100 | Day 200 | Day 300 | 1st anniversary | Day 1000 |
|---|---|---|---|---|---|
| Thu, Dec 25, 2025 | Fri, Apr 3 | Sun, Jul 12 | Tue, Oct 20 | Fri, Dec 25 | Tue, Sep 19, 2028 |
| Thu, Jan 1 | Fri, Apr 10 | Sun, Jul 19 | Tue, Oct 27 | Fri, Jan 1, 2027 | Tue, Sep 26, 2028 |
| Sat, Feb 14 | Sun, May 24 | Tue, Sep 1 | Thu, Dec 10 | Sun, Feb 14, 2027 | Thu, Nov 9, 2028 |
| Sat, Mar 14 | Sun, Jun 21 | Tue, Sep 29 | Thu, Jan 7, 2027 | Sun, Mar 14, 2027 | Thu, Dec 7, 2028 |
| Thu, May 14 | Fri, Aug 21 | Sun, Nov 29 | Tue, Mar 9, 2027 | Fri, May 14, 2027 | Tue, Feb 6, 2029 |
Dates without a year are in 2026, and all values count the start date as day 1.
You can know the weekday in advance
Weekdays repeat every 7 days, so the weekday shifts by the remainder when the number of days added to the start date is divided by 7. With the start date as day 1, it works out like this.
| Anniversary | Days added | Weekday shift | If you got together on a Saturday |
|---|---|---|---|
| Day 100 | 99 | 1 day later | Sunday |
| Day 200 | 199 | 3 days later | Tuesday |
| Day 300 and day 1000 | 299 and 999 | 5 days later | Thursday |
| 1st anniversary | 365 (366 if it passes February 29) | 1 day later (2 days later) | Sunday (Monday) |
If you got together on a weekend, day 100 tends to land on a weekend too, while days 200 and 300 move to weekdays. For anything that needs a reservation, check the weekday first.
Counting from day 1 or from day 0
If another calculator gives a result one day off, the usual cause is how the first day is counted. Korean couples usually count the start date as day 1, while some other calculators count the days that have passed since the start date (day 0), which gives a date one day later.
| Start 2026-01-01 | Start date as day 1 (default) | Counting from day 0 |
|---|---|---|
| 100 | Fri, Apr 10 | Sat, Apr 11 |
| 200 | Sun, Jul 19 | Mon, Jul 20 |
| 300 | Tue, Oct 27 | Wed, Oct 28 |
| 1000 | Tue, Sep 26, 2028 | Wed, Sep 27, 2028 |
| 1st anniversary | Fri, Jan 1, 2027 | Fri, Jan 1, 2027 |
For contracts and legal deadlines, the period follows the counting rules set by each country's law, so use the Date Calculator rather than this one.
Start dates on the 31st or February 29
Months and anniversaries use the same calendar date, and in a month that does not have that date, the last day of the month is used.
| Start date | Milestone | Date |
|---|---|---|
| 2026-01-31 | Months 1, 2 and 3 | 2026-02-28 · 2026-03-31 · 2026-04-30 |
| 2026-01-31 | 1-year anniversary · 13 months | 2027-01-31 · 2027-02-28 |
| 2024-02-29 | Anniversaries 1, 2 and 3 | 2025-02-28 (Fri) · 2026-02-28 (Sat) · 2027-02-28 (Sun) |
| 2024-02-29 | Anniversaries 4 and 8 | 2028-02-29 (Tue) · 2032-02-29 (Sun) |
Special dates are for reference
The special dates in the list are Valentine's Day (February 14), Christmas Eve (December 24) and Christmas Day (December 25). Many couples like to mark them, but they are not official anniversaries and no couple has to mark them. They are kept in a separate view so they do not stand in for the dates that are yours alone.
Common mistakes
- Working out day 100 as the start date plus 100 days: counting the start date as day 1, that lands one day late. Day 100 is the start date plus 99 days.
- Treating the first anniversary as day 365: it is the same date next year, which is day 366 (day 367 if it passes February 29).
- Starting from different dates: if the day you confessed and the day you decided to be a couple differ, your anniversaries are off by a day or more. Agree on one start date first.
- Counting months in blocks of 30 days: a month is not 30 days, it is the same date the next month. With February in between it is 28 or 29 days, and with a 31-day month it is 31 days.
Limits and notes
- Today is taken from your device's date. If you are abroad and the date differs, the result can be a day off.
- Only the Gregorian calendar is calculated. Check lunar-calendar anniversaries separately.
- The start date can be any date from January 1, 1900 up to today, and the day-N finder goes up to 36,500. The list shows up to day 10,000 and the 60th anniversary.
- The calendar file sets no reminder time, so turn on reminders in your calendar app after importing it.
Basis The example values in this article were calculated on the Gregorian calendar.
Source
- 01RFC 5545 - Internet Calendaring and Scheduling Core Object Specification (iCalendar)The calendar file saves each anniversary as an all-day event (DTSTART;VALUE=DATE)
- 02U.S. Naval Observatory: Introduction to CalendarsGregorian leap-year rule (every 4 years, except century years not divisible by 400), used for February 29 start dates
Frequently asked questions
When is day 100 of a relationship?
The start date counts as day 1, so day 100 is the start date plus 99 days. If you got together on January 1, 2026, day 100 is Friday, April 10, 2026, day 200 is Sunday, July 19 and day 300 is Tuesday, October 27.
Why is the start date counted as day 1?
Korean couples usually count the day they got together as day 1. Some other calculators count the days that have passed since then (day 0), which gives a result one day later. To count from day 0, turn off the switch for counting the first day as day 1. For contracts and legal deadlines, each country's law defines how a period is counted, so use the Date Calculator instead.
Is the first anniversary day 365?
No. The first anniversary is the same date one year later, which is day 366 when the start date counts as day 1, or day 367 if February 29 falls in between. If you got together on January 1, 2026, day 365 is Thursday, December 31, and the first anniversary is Friday, January 1, 2027.
When is day 1000?
It is the start date plus 999 days. If you got together on February 14, 2024, day 1000 is Monday, November 9, 2026. For a day that is not in the list, such as day 1234, type the number into the "When is day N" box to get the date and the time left.
Which weekday is day 100?
With the start date as day 1, day 100 falls one day later in the week than the start date, because 99 days is 14 weeks and 1 day. Day 200 is 3 days later in the week, and days 300 and 1000 are 5 days later in the week.
What happens to months and anniversaries if we got together on the 31st or February 29?
In a month without that date, the last day of the month is used. If you got together on January 31, month 1 is February 28 (29 in a leap year) and month 2 is March 31. If you got together on February 29, 2024, the first anniversary is Friday, February 28, 2025 and the fourth is Tuesday, February 29, 2028.
Can I find out which day a particular date is?
Pick the date in the "Which day is this date" box or select it in the calendar. If you got together on January 1, 2026, Christmas Day that year (December 25) is day 359.
Can I add the anniversaries to my phone's calendar?
Press "Save to calendar (.ics)" to save a file with the day, month and year anniversaries of the next 3 years as all-day events. Import it into Google Calendar, Apple Calendar or Outlook, and set reminders in the calendar app.