Anniversary Calculator and Countdown
Enter a start date such as the day you met, married or opened a business, and get the dates and weekdays of the 100-day, 200-day … 1000-day, monthly and yearly milestones, plus how far away each one is from today. You can also count down the days to an event like a concert or holiday. Everything is processed in your browser. To simply measure the gap between two dates, use the Date Calculator; for working days only, try the Business Day Calculator.
🔒 Runs in your browser · Your data is never sent to a server
Start date and reference date
Milestone list
List type| Milestone | Date | From reference date |
|---|
Look up any number of days
Countdown to an event
How to use
- Enter the "Start date" such as the day you met or opened; the reference date defaults to today.
- Switch the list between days, months and years to see each milestone date and how far away it is.
- Toggle "Count the start date as day 1" if you count days a different way.
- Enter an event date to see how many days are left.
Notes
- With "Count the start date as day 1" on, the start date is day 1 and day 100 is 99 days later. With it off, the start date is day 0 and 100 days after is exactly 100 days later.
- Yearly anniversaries fall on the same month and day as the start date and do not depend on that setting. For a Feb 29 start in a non-leap year, February 28 is used by default; you can switch to March 1.
- When a later month has no matching day (for example one month after January 31), the last day of that month is used.
- All calculations use calendar dates, so daylight saving time and time zones do not affect the result. The Gregorian calendar and years 1 to 9999 are supported.
Glossary
Inclusive vs. exclusive counting
Inclusive counting treats the start date as day 1; exclusive counting treats the following day as day 1. Legal period calculations often exclude the first day, while personal anniversaries are frequently counted inclusively.
Corresponding day
The day that has the same day-of-month as the start date in a later month or year. When the month has no such day, the last day of that month is normally used.
FAQ
How many days after we met is our 100-day anniversary?
It depends on how you count. If the day you met is day 1, day 100 is 99 days later; if it is day 0, the 100-day mark is 100 days later. Use the "Count the start date as day 1" option to switch.
What date is a yearly anniversary of February 29?
In years that are not leap years there is no February 29, so February 28 is used by default. You can switch to March 1. In leap years the anniversary stays on February 29.
What is one month after January 31?
February has no 31st, so the last day of that month is used (February 28, or 29 in a leap year). Each milestone is calculated from the start date, so two months after January 31 is March 31.
Does the countdown to an event include the event day?
It shows the calendar difference from the reference date. If today is the 12th and the event is on the 15th, it says 3 days; on the day itself it says the event is today.
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