Age calculator - date difference

Step-by-step example: where 41 y 3 m 28 d comes from

Say the date of birth is 17.05.1985 and the end date is 14.09.2026. First the years are subtracted (2026 - 1985 = 41), then the months (9 - 5 = 4) and finally the days (14 - 17 = -3).

The day difference is negative, so one month is borrowed: the months drop to 3 and the length of the previous month is added to the days. The month before September is August with 31 days, so -3 + 31 = 28. The result is 41 years, 3 months and 28 days.

At the same time the calculator shows the totals: 495 months, 2156 weeks and 15,095 days. These come straight from the gap between the dates and do not depend on how the months and days were split above.

Three more calculations with different dates

A date difference does not have to be a person's age. The same calculation measures length of service, how long a relationship has lasted, a pet's age or the time left until an event.

• 01.09.2008 to 14.09.2026: 18 y 0 m 13 d, a total of 216 months and 6587 days.
• 15.03.2019 to 14.09.2026: 7 y 5 m 30 d, a total of 89 months and 2740 days.
• 14.09.2026 to 21.06.2027: 0 y 9 m 7 d, a total of 40 weeks and 280 days. With a future end date the calculator works as a countdown.

The birthday boundary and 29 February

The calculator measures the gap between two dates rather than counting days with both ends included. Someone born on 14.09.2006 is therefore exactly 20 y 0 m 0 d on 14.09.2026, while one day earlier, on 13.09.2026, the result is 19 y 11 m 30 d. Full years change exactly on the birthday date.

A leap-day birthday is a special case. For a birth date of 29.02.2000 the calculator shows 0 y 11 m 30 d on 28.02.2001 and exactly 1 year on 01.03.2001. In a non-leap year, someone born on 29 February turns a year older on 1 March according to the calculator.

What the totals really mean

The total days figure is the number of days between start and end, not counting the start day. If you need a period length with both the first and last day included (say, a contract valid from the 1st to the 10th), add one day to the result.

Weeks are rounded down to whole weeks: 15,095 days is 2156 full weeks and 3 days. The month total also counts only whole months, that is years times 12 plus the remaining months.

Total days is the least ambiguous figure. Years and months depend on the uneven length of months while days do not, so use days when comparing deadlines.

End-of-month dates and other limitations

When the start date is the last day of a month, 'one month later' is not always clearly defined. For example, 31.01.2026 to 28.02.2026 gives 0 m 28 d, because February has no 31st. Different tools may display such gaps differently, so check the total days for an exact deadline.

• The Today button sets the end date to the current day. To get your current age, pick the date of birth and press that button.
• The calculation is date-based: time of birth and time zones do not affect the result.
• The order of the dates does not matter, as the later and earlier date are swapped automatically if needed.
• The result says nothing about legal deadlines. If a right starts at a certain age, check the exact rule with the relevant law or authority.