How Many Days in a Year? Leap Years Explained

How many days in a year, month by month

February holds the whole difference between the two kinds of year: 28 days in a common year and 29 in a leap year. Seven months have 31 days, and April, June, September and November have 30.

Month	Days in a common year	Days in a leap year
January	31	31
February	28	29
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
Total	365	366

How many weeks in a year?

A year is 52 weeks and 1 day, or 52.14 weeks. A leap year is 52 weeks and 2 days, or 52.29 weeks.

Unit	Common year (365 days)	Leap year (366 days)
Weeks	52 weeks and 1 day (52.14)	52 weeks and 2 days (52.29)
Hours	8,760	8,784
Minutes	525,600	527,040
Seconds	31,536,000	31,622,400

The leftover day makes one weekday occur 53 times instead of 52: the weekday of January 1, plus that of January 2 in a leap year. 2026 began on a Thursday, so it has 53 Thursdays, and an employer that pays every Thursday runs 53 weekly payrolls that year. Biweekly pay usually gives 26 paydays, but a year has 27 when its first payday falls on January 1, or on January 1 or 2 in a leap year.

The same leftover day moves every date 1 weekday later from one year to the next, or 2 later when a February 29 comes between.

Numbered weeks follow a different count. Under ISO 8601, the international standard for week numbers, weeks run Monday to Sunday and a year has 52 or 53 of them. It has 53 when it starts on a Thursday, or when it is a leap year that starts on a Wednesday, which happens in 71 of every 400 years. 2020, 2026 and 2032 are 53-week years.

Weekdays and business days in a year

A common year has 261 weekdays (Monday to Friday) when it starts on a weekday, and 260 when it starts on a Saturday or Sunday. A leap year that starts on Monday through Thursday has 262.

Business days are fewer, because federal holidays fall on some of those weekdays. 2026 has 261 weekdays, and its 11 federal holidays leave 250 business days. 2027 has 249: New Year’s Day 2028 is a Saturday, so it is observed on Friday, December 31, 2027. The business day counter does the same subtraction for any range of dates.

Why leap years exist

The solar year, the time the seasons take to come round again, is about 365.242 days long, according to the National Institute of Standards and Technology (NIST). A calendar of exactly 365 days would fall behind the seasons by almost a quarter of a day each year, or about 24 days each century.

A leap day every 4 years puts back 0.25 days a year, which slightly overcorrects. The Gregorian calendar, the civil calendar in the United States, removes 3 leap days every 400 years. That leaves 97 leap years in every 400 and an average year of 365 + 97 ÷ 400 = 365.2425 days.

Leap seconds solve a different problem. They keep atomic clock time in step with the Earth’s rotation, and they never change the number of days in a year.

The leap year rule: divisible by 4, 100 and 400

A year is a leap year if it divides evenly by 4, except century years, which must also divide evenly by 400. The rule takes up to three checks:

1. If the year is not divisible by 4, it is a common year with 365 days.
2. If the year is divisible by 4 but not by 100, it is a leap year with 366 days.
3. If the year is divisible by 100, it is a leap year only if it is also divisible by 400.

Century years show the rule most clearly. A dash means an earlier check already settled the answer.

Year	Divisible by 4	Divisible by 100	Divisible by 400	Leap year	Days
1900	Yes	Yes	No	No	365
2000	Yes	Yes	Yes	Yes	366
2024	Yes	No	—	Yes	366
2025	No	—	—	No	365
2100	Yes	Yes	No	No	365
2400	Yes	Yes	Yes	Yes	366

Is 2026 a leap year?

2026 is a common year with 365 days. 2026 ÷ 4 = 506.5, so 2026 is not divisible by 4. The last leap year was 2024, and the next is 2028.

2028 is a leap year: 2028 ÷ 4 = 507, and it is not a century year, so February 2028 has 29 days and February 29 falls on a Tuesday. Leap years then come every 4 years until 2096. 2100 fails the 400 test, so the leap year after 2096 is 2104.

Checking a year in Excel or Google Sheets

With a year such as 2028 in cell A2, these formulas answer the questions on this page.

Question	Formula	Result for 2028
Is it a leap year?	=OR(MOD(A2,400)=0,AND(MOD(A2,4)=0,MOD(A2,100)>0))	TRUE
How many days?	=DATE(A2+1,1,1)-DATE(A2,1,1)	366
How many weekdays?	=NETWORKDAYS(DATE(A2,1,1),DATE(A2,12,31))	260
How many ISO weeks?	=ISOWEEKNUM(DATE(A2,12,28))	52

Excel treats 1900 as a leap year, a choice kept for compatibility with the older Lotus 1-2-3, so its date functions report a February 29, 1900 that never existed. The MOD formula in the first row gets 1900 right, returning FALSE.

Where the rule came from

Julius Caesar’s calendar of 45 B.C. added a leap day every 4 years, which NIST describes as 365 days plus a leap day every fourth year. That average of 365.25 days ran about 11 minutes a year too long, and by 1582 the calendar was 10 days off. Pope Gregory XIII’s reform that year dropped 10 days and added the century exception that is still in use.

February 29 in date math

Someone born on February 29 has a calendar birthday only in leap years. The birthday countdown uses February 28 in common years by default, with March 1 as an option.

From March 1 on, every date’s day-of-year number is 1 higher in a leap year: March 1 is day 60 in a common year and day 61 in a leap year. The day-of-year counter and the count of days left in 2026 both allow for it. A date range that includes February 29 is 1 day longer, which the guide on counting days between dates works through.

A fixed count of days lands a day earlier when it crosses February 29. A 90-day count from January 15 ends on April 15 in 2026 but on April 14 in 2028, a leap year. Finding the date 90 days from today works the same way, with the leap day counted whenever the span crosses it.