How Many Days Are in Each Month of a Leap Year?
A leap year contains 366 days instead of the usual 365. The extra day is added to February, giving that month 29 days rather than 28. Every other month keeps the same length it has in a common year.
This small adjustment helps the calendar stay aligned with Earth’s trip around the Sun. A solar year is slightly longer than 365 days, so the calendar periodically adds a day to prevent seasons and dates from gradually drifting apart.
Knowing the length of every month in a leap year is useful for planning schedules, calculating elapsed time, checking deadlines, and working with annual budgets. It also makes it easier to understand why some date calculations differ by one day from year to year.
The leap-year month pattern
The first month of a leap year, January, has 31 days. February has 29, March has 31, April has 30, May has 31, and June has 30. The second half follows the familiar sequence: July has 31, August has 31, September has 30, October has 31, November has 30, and December has 31.
The full sequence is therefore 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, and 31. Adding these values produces 366 days. For a quick reference covering both common and leap years, the month day counts page provides a practical overview.
| Month | Days in a leap year | Days in a common year |
|---|---|---|
| January | 31 | 31 |
| February | 29 | 28 |
| March | 31 | 31 |
| April | 30 | 30 |
| May | 31 | 31 |
| June | 30 | 30 |
| July | 31 | 31 |
| August | 31 | 31 |
| September | 30 | 30 |
| October | 31 | 31 |
| November | 30 | 30 |
| December | 31 | 31 |
Why February has 29 days
February receives the extra day because it is the shortest month. Adding a day there creates the required 366-day year without changing the established lengths of the other months. This arrangement comes from the Gregorian calendar, the calendar system used in most countries today.
The extra date is February 29, commonly called leap day. It appears after February 28 and before March 1. As a result, a birthday, anniversary, or deadline that falls on February 29 requires special handling in years when that date does not exist.
How the Gregorian leap-year rule works
Under the Gregorian rules, a year is a leap year if it is divisible by four. For example, 2024, 2028, and 2032 all have 366 days. Years that cannot be divided evenly by four are common years with 365 days.
There is an exception for century years. A year ending in two zeroes must also be divisible by 400 to qualify. Thus, 2000 was a leap year, while 1900 was not. The same rule means 2100 will be a common year, but 2400 will be a leap year.
This formula keeps the calendar closely synchronized with the solar year. Without century exceptions, the calendar would add slightly too many days over long periods and gradually shift away from the seasons.
Counting dates across a leap year
For calculations within one month, the correct month length matters immediately. From February 1 to March 1 in a leap year, 29 days pass. In a common year, the same date range spans 28 days. This one-day difference affects payroll periods, subscription cycles, project schedules, and age calculations.
A leap year also changes the day number assigned to every date after February 28. March 1 is day 61 in a leap year but day 60 in a common year. By December 31, the leap-year date count reaches 366, while a common year ends at day 365.
When calculating business days, weekends and public holidays must be considered separately from the total number of calendar days. A leap day can add one calendar day, but whether it adds a working day depends on which weekday February 29 falls on and on the holiday calendar being used.
Leap years in broader calendar comparisons
The extra day applies to Earth’s Gregorian calendar, not to every calendar or planetary time system. A year on Pluto, for instance, lasts far longer than an Earth year, so comparisons between planetary years and calendar years require a different basis. The explanation of a Pluto year illustrates why the word “year” depends on the orbit being measured.
For ordinary date work, however, the Gregorian pattern is consistent enough to use with confidence. Years from 2000 through 2050 can be checked by applying the divisible-by-four rule and remembering the century exception. Within that range, 2000, 2004, 2008, and every fourth year afterward through 2048 are leap years.
A calendar lookup is especially helpful when a calculation crosses February. It prevents common errors such as treating February as having 28 days every year or assuming that a year divisible by four is always a leap year.
Practical ways to check month lengths
A simple memory pattern can help: the months through July alternate between 31 and 30 days, except February, while August begins another run of 31-day months followed by alternating 30- and 31-day months. The familiar knuckle method also identifies 31-day months, with February remaining the special case.
For accurate planning, use these checks:
- Confirm whether the year is common or leap before counting dates.
- Treat February as 29 days only when the Gregorian leap-year rule applies.
- Count the starting and ending dates consistently in elapsed-time calculations.
- Separate calendar days from business days, weekends, and holidays.
- Verify dates after February 28 when comparing annual schedules.
The result is straightforward: a leap year has 31 days in January, 29 in February, 31 in March, 30 in April, 31 in May, 30 in June, 31 in July, 31 in August, 30 in September, 31 in October, 30 in November, and 31 in December. Use this pattern whenever you need to check a deadline, calculate elapsed time, or build a reliable yearly schedule.