A year has 365 days, a leap year 366. So far, so familiar. But why are there leap years at all, why will 2100 not be one, and what does 29 February mean when you count days, deadlines or working days? Here are the answers in brief.
The figures at a glance
| Common year | Leap year | |
|---|---|---|
| Days | 365 | 366 |
| Weeks | 52 weeks and 1 day | 52 weeks and 2 days |
| Hours | 8,760 | 8,784 |
| February | 28 days | 29 days |
| Examples | 2026, 2027, 2029 | 2024, 2028, 2032 |
The leap year rule
The Gregorian calendar in use today has a three-step rule:
- Every year divisible by 4 is a leap year: 2024, 2028, 2032.
- Exception: full centuries, i.e. years divisible by 100, are not leap years: 1900, 2100, 2200.
- Exception to the exception: years divisible by 400 are leap years after all: 1600, 2000, 2400.
That is why 2000 was a leap year and 2100 will not be one. The next leap years are 2028, 2032, 2036 and 2040.
Why leap years exist
The Earth takes about 365.2422 days to orbit the Sun, measured from one spring equinox to the next. A calendar with exactly 365 days would drift by more than 24 days after 100 years, and spring would slowly move into summer.
The Julian calendar therefore added one day every fourth year from antiquity onwards. That gave an average year of 365.25 days, about 11 minutes too long. By the 16th century this had added up to around ten days. With the Gregorian calendar reform of 1582, Thursday, 4 October, was followed directly by Friday, 15 October 1582. Since then, three leap days are dropped every 400 years. The average calendar year thus has 365.2425 days and is only off by about one day in roughly 3,000 years. The Protestant territories of Germany only adopted the new calendar in 1700.
What the leap day means when counting days
Periods across the end of February: from 1 February to 1 March there are exactly 28 days in 2027, but 29 days in 2028. When counting by hand, the leap day is easily forgotten. The days calculator takes it into account automatically.
Monthly and yearly deadlines: deadlines in months or years run from date to date, not over a fixed number of days. One year from 1 March 2027 ends when 29 February 2028 expires, and is therefore 366 days long. If a one-month deadline would end on 29, 30 or 31 February, the last day of February applies (§ 188(3) BGB). More on this in the article Calculating deadlines under the BGB.
Birthday on 29 February: anyone born on a leap day celebrates on 28 February or 1 March in common years. What applies legally is explained in the article Born on 29 February at the age calculator.
Weekdays: because 365 days are 52 weeks and one day, a date moves forward by one weekday each year, and by two after a leap day. 1 January 2026 was a Thursday, 1 January 2027 is a Friday, 1 January 2028 a Saturday and, after the leap year, 1 January 2029 a Monday.
More days does not mean more working days
A leap year has one more day, but not necessarily more working days. 2028 has 366 days, starts on a Saturday and ends on a Sunday. From Monday to Friday there are 260 days, one fewer than in 2026 and 2027. Because 8 of the 9 nationwide holidays also fall on a weekday in 2028, only 252 working days remain nationwide, and only 249 in Bavaria. In 2027 there are 256 nationwide. The figures for all states are in the article Working days 2027 by German state and in the table next to the days calculator.
Conclusion
A year has 365 days, a leap year 366. Every year divisible by 4 is a leap year, except full centuries that are not divisible by 400. The next leap year is 2028; 2100 will not be one. For your own periods, the days calculator counts the leap day automatically.
As of 26 October 2026.