Anniversary Calculator
A wedding on June 15, 2021 has marked 5 years by July 21, 2026, with the next anniversary 329 days away. This anniversary calculator takes any start date and tells you how many full years have passed, how many days since the last anniversary, and exactly when the next one lands on the calendar. It works for weddings, work anniversaries, sobriety milestones, adoption days, business founding dates, and any date you want to track year after year.
Quick answer
Enter a start date and a today date. The calculator finds the number of completed years between them and shows the last and next anniversary dates.
Years completed
5 years
Days since last anniversary
36
Days until next anniversary
329
Last anniversary
2026-06-15
Next anniversary
2027-06-15
What this tells you
- •Enter a start date and a today date. The calculator finds the number of completed years between them and shows the last and next anniversary dates.
- •The years count is how many full anniversaries have passed, not a rounded number. If you are 6 months short of the next year, the count stays at the lower whole number.
- •Days until next counts from today to the next time the month and day match the start date. It uses calendar rules so leap years and month lengths are handled correctly.
- •Days since last counts backward from today to the most recent past occurrence of that month and day.
- •If today is the anniversary date, the result shows 0 days since and the years count reflects the completed period.
- •Leap-year start dates such as February 29 are read correctly. In non-leap years the next anniversary falls on March 1, matching the common convention.
How to Use
- 1Enter the original date in the Start date field. This is the date you want to track, such as a wedding date, a start-at-work date, or a quit date.
- 2Enter today's date or the date you are checking from. The result counts from this date, so changing it lets you look forward or backward to a specific point.
- 3Read the years completed field. This is the count of full anniversaries that have passed, the number you would use in conversation.
- 4Check the days since last anniversary to see how recently the date passed. This is helpful for thank-you notes or late acknowledgments.
- 5Check the days until next anniversary to plan ahead. This number counts calendar days from today to the next matching month and day.
- 6Use the next anniversary date to set a calendar reminder or to coordinate with other people who need the same date for planning.
How It Works
Formula
years = today year - start year (adjusted if today is before the anniversary month/day)The calculator finds completed years by comparing the start year to the current year, then backs off by one if today has not yet reached the anniversary month and day in the current year. The next anniversary is the next calendar date with the same month and day as the start date that falls on or after today. The last anniversary is the most recent past calendar date matching the start month and day. Both use standard JavaScript date handling with the full calendar month and year context, so February 29 in a leap year is handled properly and the next occurrence after a leap-year start date in a non-leap year falls on March 1.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Wedding anniversary after 5 years
Five full Junes have passed since June 2021. The most recent anniversary was June 15, 2026, which is 36 days ago from July 21. The next one is June 15, 2027.
First anniversary approaching
Less than one full year has passed, so the years count is 0. The last anniversary was September 10, 2025, and the next is September 10, 2026, about 51 days away.
Today is the anniversary
When today matches the start month and day, the years count is the completed number and the days-since field reads zero.
Leap-year start date
For a February 29 start date, the anniversary in a non-leap year lands on March 1. The years count still uses completed calendar years.
Anniversary Counts from Common Start Dates
Sample counts from July 21, 2026 for various start dates.
| Start date | Years | Days until next | Next date |
|---|---|---|---|
| June 15, 2021 | 5 | 329 | Jun 15, 2027 |
| September 10, 2025 | 0 | 51 | Sep 10, 2026 |
| January 1, 2020 | 6 | 164 | Jan 1, 2027 |
| December 25, 2018 | 7 | 157 | Dec 25, 2026 |
Common mistakes
- Counting years by subtracting the start year from the current year without checking whether the month and day have passed yet.
- Forgetting that leap-year dates such as February 29 shift to March 1 in non-leap years for anniversary tracking.
- Confusing the days-since count with the years count. Days since last resets to zero after each anniversary, while years keeps accumulating.
- Using the wrong direction when planning. Days until next counts forward from today, while days since last counts backward.
Embed this calculator on your site
Drop this single line where you want the calculator to appear. It is responsive, mobile-friendly, resizes automatically, and is free to use with attribution.
<script src="https://calctide.com/embed.js" data-tool="anniversary-calculator" async></script>Preview the embed at /embed/anniversary-calculator/.