Days In Months

What the days in months tool does

Months are not all the same length, and the one that keeps changing is February. This tool clears that up. Enter a year and it lists how many days each month has, from January through December, and crucially it gets February right for that exact year, 28 days in a normal year and 29 in a leap year.

It saves you second-guessing whether a particular February had 28 or 29 days, which matters more often than you would think once payroll cycles and date checks are involved.

How to use it

1. Enter Year. Type the year you want to check.

Press Calculate and it lists all twelve months with their day counts for that year.

How it works out each month

Most of the work is already decided, because eleven of the twelve months never change length. Seven of them have 31 days and four have 30, year in and year out. February is the only one that moves. So the tool fills in the fixed months straight away, then checks the leap-year rule against the year you entered to decide whether February gets 28 days or 29, and lays the whole year out.

The month-length pattern, and two ways to remember it

The lengths fall into a simple pattern: January 31, February 28 or 29, March 31, April 30, May 31, June 30, July 31, August 31, September 30, October 31, November 30, December 31. There are two old tricks for keeping it straight without a tool.

The first is the rhyme: "Thirty days hath September, April, June, and November; all the rest have thirty-one, except February alone." Name those four 30-day months and February, and everything else is a 31.

The second is the knuckle trick. Make a fist and run across your knuckles and the dips between them. Each knuckle is a 31-day month and each dip is a shorter one, starting with January on the first knuckle. When you reach the end of one hand at July, start again on the first knuckle of the other hand for August, and the pattern keeps working.

Why February is the odd one out

February changes because of how the calendar keeps step with the seasons. A year is very close to 365 and a quarter days, so to stop the calendar drifting, an extra day is added every four years, and February is where it goes. That gives a leap year of 366 days. The rule is not quite "every four years," though. A year is a leap year if it divides by 4, except for century years, which only count if they also divide by 400. That is why 2024 has a 29-day February, 2023 has 28, the year 1900 had 28, and the year 2000 had 29. The tool applies that full rule, so the February it shows you is always right for the year you picked.

Where it comes in handy

Anywhere the exact length of a month matters. Payroll and billing cycles that run by the calendar month land differently in a 31-day month than a 28-day one. Scheduling and planning need the real end of a month. And it is a quick sanity check when validating a date, since it tells you in a glance that there is no 30th of February to worry about.

Questions people ask

How many days does February have this year?

It depends on whether the year is a leap year. February has 29 days in a leap year and 28 otherwise. Enter the year and the tool shows you which it is.

Which months have 31 days, and which have 30?

Seven months have 31 days: January, March, May, July, August, October, and December. Four have 30: April, June, September, and November. February has 28 or 29.

How do I know if a year is a leap year?

A year is a leap year if it divides evenly by 4, except for century years, which must also divide by 400. So 2024 and 2000 are leap years, but 1900 and 2100 are not.

Is there an easy way to remember the lengths?

Two, in fact. The rhyme "thirty days hath September, April, June, and November" names the short months, and the knuckle trick lets you read them off your hand, each knuckle a 31-day month and each dip a shorter one.

References

1. U.S. Naval Observatory, Astronomical Applications Department: Leap Years. https://aa.usno.navy.mil/faq/leap_years