Seven months have 31 days (January, March, May, July, August, October and December), four have 30 days (April, June, September and November), and February has 28, or 29 in a leap year. Altogether that's 365 days, or 366 in a leap year.
Days and numbers for every month
| No. | Month | Abbr. | Days | Day of year it starts (common / leap) |
|---|---|---|---|---|
| 1 | January | Jan | 31 | 1 / 1 |
| 2 | February | Feb | 28 (29) | 32 / 32 |
| 3 | March | Mar | 31 | 60 / 61 |
| 4 | April | Apr | 30 | 91 / 92 |
| 5 | May | May | 31 | 121 / 122 |
| 6 | June | Jun | 30 | 152 / 153 |
| 7 | July | Jul | 31 | 182 / 183 |
| 8 | August | Aug | 31 | 213 / 214 |
| 9 | September | Sep / Sept | 30 | 244 / 245 |
| 10 | October | Oct | 31 | 274 / 275 |
| 11 | November | Nov | 30 | 305 / 306 |
| 12 | December | Dec | 31 | 335 / 336 |
The last column is handy for working out the day of the year: October 3 is day 274 + 2 = 276 in a common year.
The "30 days hath September" rhyme
The traditional English rhyme, dating back to at least the 1500s, goes:
Thirty days hath September,
April, June and November.
All the rest have thirty-one,
Excepting February alone,
Which has but twenty-eight days clear,
And twenty-nine in each leap year.
Many versions exist. As long as you remember the first two lines, you can work out the rest.
The knuckle trick
If rhymes aren't your thing, use your hands:
- Make a fist with one hand and look at your knuckles.
- Starting with the first knuckle (index finger), name the months in order: each knuckle is January, March, May…, and each dip between knuckles is February, April, June…
- When you reach the last knuckle (July), start again on the first knuckle with August, or continue on your other hand.
- Knuckle months have 31 days; dip months have 30 (except February).
The trick works because July and August, both 31 days, land on knuckles back to back.
Why are months different lengths?
Our calendar descends from the Roman calendar. The early Roman year had 10 months and began in March, which is why September, October, November and December come from the Latin for seven, eight, nine and ten. January and February were added later, and February, at the end of the year, absorbed the shortfall.
When Julius Caesar reformed the calendar in 46 BC, he set the month lengths close to what we use today, with February getting the leap day every four years. A popular story claims Augustus stole a day from February so that August would match July, but historians consider this a medieval myth. In 1582, Pope Gregory XIII refined the leap-year rule to create today's Gregorian calendar. Read more in how leap years work.
Months with five weekends and other quirks
- A 31-day month that starts on a Friday has five Fridays, five Saturdays and five Sundays. In 2027, that happens in January and October.
- February is the only month that can fit on exactly four calendar rows, when it has 28 days and starts on the first day of your week.
- July and August are the only consecutive months that both have 31 days, apart from December and January across the new year.
- The average month is 30.44 days, or about 4.35 weeks.
Writing dates with month numbers
In the US, dates are usually written month/day/year: 10/03/2026 is October 3, 2026. Most of the world writes day/month/year (03/10/2026), and the international standard, ISO 8601, uses year-month-day: 2026-10-03. The ISO format is unambiguous and sorts correctly, so it's a good choice for file names and international communication.
See any month at a glance: the 2026 calendar shows every month with holidays and week numbers, and pages like days until the end of October count down to month end.
Frequently asked questions
How many months have 31 days?
Seven: January, March, May, July, August, October and December.
Which months have 30 days?
April, June, September and November.
What month is number 9?
September. Month 10 is October, 11 is November and 12 is December.
How many days are in February 2028?
29, because 2028 is a leap year. Februaries in 2026 and 2027 have 28 days.