How Many Days in Each Month?

Four months have 30 days. Seven months have 31 days. February has 28 days, or 29 in a leap year. If you need to look this up more than once per year, you are not alone. "How many days in [month]" is one of the most consistently searched questions on the internet, peaking at the start of every month as people check their calendars.

The pattern is genuinely hard to memorize because there is no pattern. It is not alternating 30-31. It is not organized by season. July and August are both 31 days back to back. September through November go 30-31-30. There is a rhyme ("Thirty days hath September...") and a knuckle trick, but the fact that we need mnemonic devices for something this basic tells you everything about how poorly designed the calendar is.

The calendar we use today (the Gregorian calendar, introduced in 1582) was a patch on the Julian calendar (45 BC), which was itself a patch on the Roman Republican calendar, which started the year in March and had only 10 months. January and February were added later. The whole thing was built by committee over 2,000 years, and it shows.

📅 Days per Month Chart

✊ How Does the Knuckle Trick Work?

Make a fist. Starting from your left pinkie knuckle, count across: knuckle = 31, valley = 30 (except February). January is the first knuckle (31), February is the first valley (28/29), March the next knuckle (31), and so on. When you reach the last knuckle (July, 31), go back to the first for August (31). Both July and August have 31 days because of two consecutive knuckles. This trick has been taught to children for centuries.

📅 Why Does February Only Have 28 Days?

In the original Roman calendar, the year started in March and February was the last month. When they needed to adjust the calendar to match the solar year, February was the month that lost days. Then Julius Caesar (July) and Augustus Caesar (August) each claimed months and insisted they both have 31 days, which stole even more from February. Its been stuck at 28 ever since, with a 29th day added every 4 years as a correction.

📅 Why Do July and August Both Have 31 Days?

Roman politics. July was named after Julius Caesar and August after Augustus Caesar. Neither emperor was willing to have a shorter month than the other, so both got 31 days. The extra day had to come from somewhere, and that somewhere was February. If the Romans had been less vain, we might have a much more balanced calendar today.

📅 The 30-Day Month Is a Roman Political Compromise

The original Roman calendar had only 10 months (March through December) totaling 304 days. King Numa Pompilius added January and February around 713 BC to fill the winter gap. The months alternated between 29 and 30 days (Romans considered even numbers unlucky), giving a 355-day year. Priests were supposed to add extra days periodically to keep the calendar aligned with seasons, but they often manipulated the additions for political reasons, and by Julius Caesars time the calendar was three months out of sync with the actual seasons.