Anniversary Calculator

DateMath counts the whole years since the start date, then the whole months since the last anniversary, then the days left over, the way an age is counted. Anniversaries keep the day number of the start date: a wedding on February 29 has its anniversary on February 28 in common years, and a relationship that started on the 31st has its monthly anniversary on the last day of shorter months. Day milestones count the start date as day 0, so the 100th day is 100 days after it.

• The Gregorian calendar. DateMath treats every date as a Gregorian date, with its leap-year rule: a year divisible by 4 is a leap year, except century years not divisible by 400, so 2000 had a February 29 and 2100 will not. Source: Gregorian calendar.

DateMath's date math is tested against more than 100 cases worked out by hand. Every worked example and table on the site is computed with the same code the calculators run, so a page and its calculator can't disagree.

The anniversary calculator counts the time from a start date to today, or to any other date: a wedding for a wedding anniversary calculator or marriage anniversary calculator, the day you got together for a dating or relationship anniversary, or a first day at work for a work anniversary. It answers in years, months and days, as the relationship duration calculator people search for, and in total months, weeks and days. Then, as an anniversary date calculator, it gives the next anniversary date with the years it marks.

The method, step by step

Married June 18, 2016, on January 1, 2027:

1. Count the whole years: the last anniversary was June 18, 2026, so 10 years.
2. Count the whole months since then: up to December 18, 2026 is 6 months.
3. Count the days left: 14 days, so together 10 years, 6 months, 14 days, or 3,849 days.
4. The next anniversary is the 11th, on Friday, June 18, 2027, in 168 days: the steel anniversary in the traditional list.

A monthly anniversary falls on the same day of the month as the day you got together. The anniversary month calculator adds whole months to the start date, so a one month anniversary is the same day next month and a 6 month anniversary the same day 6 months on. When the month is shorter, it takes the month’s last day. For a couple together since January 31, 2026:

Each one is counted from the start date, never from the month before, so after a February the dates go back to the 31st or the month’s last day.

Day milestones count the start date as day 0, so the 100th day is 100 days after it. From June 1, 2025:

The calculator lists the same milestones for your own date and says which have passed. For any other number of days, add it to the start date in the date calculator.

The calculator names the anniversary from the traditional US list, as given in Wikipedia’s Wedding anniversary article. The lists differ by country and between traditional and modern versions, so treat the name as a custom, not a rule.

Married on February 29

DateMath puts a February 29 anniversary on February 28 in common years, so it stays in February, the rule the age calculator uses for birthdays. Married February 29, 2024, the 1st anniversary is February 28, 2025 (Friday), passed 1 year ago, and the real date returns in 2028. The leap year calculator explains the rule.

Work anniversary calculator

Choose Work and enter your first day: the result is your length of service in years, months and days. Started March 4, 2019, on January 1, 2027 that is 7 years, 9 months, 28 days, and the next work anniversary is March 4, 2027 (Thursday), in 62 days. Benefits and leave follow your employer’s own rules for counting service, so check those.

For a live countdown, enter the wedding or start date in the day countdown, name it and tick “Every year”: it counts to the next anniversary and moves on after each one. The half birthday and golden birthday calculators find other dates worth marking.