How Many Days Are in a Month and a Year?

Days in each month

Seven months have 31 days, four have 30, and February has 28 or 29. The long months are January, March, May, July, August, October and December. The 30-day months are April, June, September and November.

Two long months stand next to each other twice: July and August, and December and January. That is the only irregularity in an otherwise alternating pattern, and it is the part people tend to forget.

Two memory tricks

The first is the rhyme that many English speakers learn at school: thirty days have September, April, June and November, all the rest have thirty-one, except February alone. It names the four short months and treats February as the exception.

The second is the knuckle method. Make a fist and count the four knuckles and the three gaps between them. Say the months in order, starting on the first knuckle: January is a knuckle, February is a gap, March a knuckle, April a gap, May a knuckle, June a gap and July the last knuckle. Then go back to the first knuckle for August and carry on: September is a gap, October a knuckle, November a gap and December a knuckle. Every knuckle is a 31-day month and every gap is a short one.

Either method gives you any month length in a few seconds, which is useful when you count a span by hand.

How many days are in a year

An ordinary year has 365 days and a leap year has 366. A year is 52 weeks and 1 day, or 52 weeks and 2 days in a leap year, which is why the same date moves forward one weekday from year to year, and two weekdays across a leap day. New Year’s Day 2026 was a Thursday, 2027 begins on a Friday and 2028, a leap year, begins on a Saturday.

The calendar year is an approximation of the time the Earth takes to go round the sun. The Gregorian calendar, which most of the world uses for civil purposes, averages 365.2425 days per year over a 400-year cycle, by including 97 leap years in every 400 years.

The year is also 12 months, 52 or 53 weeks and four quarters, but these do not divide into each other evenly, which is why calendars have to compromise.

Quarters and half-years

A quarter is three months. In an ordinary year the first quarter has 90 days, the second 91, the third 92 and the fourth 92. In a leap year the first quarter has 91 days. The first half of an ordinary year is 181 days, and the second half is 184.

This matters for financial reporting and billing, because the quarters are not the same length. A monthly fee is the same each month, but a daily rate multiplied by days gives a different total per quarter.

The average month is 30.44 days, which is 365.2425 divided by 12. It is the figure to use when you need to convert months to days and a rough answer is acceptable. For an exact answer, count the actual months.

Why February is short

The calendar of the Roman republic had 355 days and added a month from time to time to keep the seasons in place. Julius Caesar reformed it in 45 BC to a year of 365 days with an extra day every four years. February was the last month of the old Roman year, which made it the natural place for corrections, and that is why it is the month whose length changes.

The short length is a leftover from that history, not a planned feature. The other months were set at 29, 30 or 31 days, and February kept what remained.

Many popular accounts add details about emperors taking days from February to lengthen their own months. Historians treat these stories as doubtful, so it is safer to stay with the general account of the Roman calendar reforms.

Months in calculations: what to use

If a rule says 30 days, use exactly 30 days. If it says one month, use the calendar, so that one month from 15 January is 15 February. If a rule uses a 360-day year with 30-day months, which some financial calculations do, use that convention as stated.

When you need a rough conversion, use 30 days per month, 91 days per quarter and 365 days per year, and add a note that the result is approximate. For anything that matters, use dates and let the calculator count the real days.

A common error is to multiply 30 by the number of months to find an end date. Six months of 30 days is 180 days, but six calendar months after 31 August 2026 is 28 February 2027, which is 181 days later. The two methods differ, and the right one depends on how the rule is written.

Using the calculator

To find the length of a particular month, enter its first and last day on the days-between tab and tick the box to include the end date. Or enter the first day of the month and the first day of the next, and read the days.

To see how many days are left in a year, enter a date on the Day of the week tab. The calculator shows the day of the year, the days left in the year, the days in that month and whether the year is a leap year.