Sequence of Months: Order, Origins, and Quick Tricks

This article answers the question “What is the sequence of months?” directly: the months in order are January, February, March, April, May, June, July, August, September, October, November, and December. This 12-month sequence forms the Gregorian calendar used by most of the world today, and each month has a specific number of days (28, 30, or 31) that repeats every year.

Formula

The sequence itself is not a mathematical formula but a fixed ordered list. However, you can express the month name as a lookup function: MonthName(n) returns the nth item in the list [January, February, March, April, May, June, July, August, September, October, November, December], where n is an integer from 1 to 12. For n = 1, the result is January; for n = 12, the result is December. The number of days in month n follows a separate rule (see below).

Worked Example

Using the default value of 1 for the month number, the lookup gives:

• n = 1 → 1st item in the list = January

So the output is January. If you enter 6, the output is June; if you enter 12, the output is December.

Background: Why 12 Months?

The 12-month year comes from ancient calendars based on lunar cycles. A lunar month (one full cycle of the Moon’s phases) is about 29.5 days, and 12 of those make roughly 354 days—about 11 days short of a solar year (365.25 days). Early Roman calendars had 10 months (starting with March), but the later Julian and then Gregorian calendars standardized the 12-month sequence we use today. The names themselves trace back to Roman gods, numbers, and Latin words:

• January – from Janus, Roman god of doorways
• February – from Februa, a Roman purification festival
• March – from Mars, god of war
• April – from Aphrodite (Greek) or the Latin aperire (to open)
• May – from Maia, goddess of growth
• June – from Juno, queen of the gods
• July – from Julius Caesar
• August – from Augustus Caesar
• September – from Latin septem (seven, originally the 7th month)
• October – from octo (eight)
• November – from novem (nine)
• December – from decem (ten)

September through December are named for numbers 7–10 because the old Roman calendar started in March.

How the Sequence Works: Days in Each Month

Each month has a fixed number of days, and the pattern is easy to memorize with a knuckle trick or a rhyme. The days are:

• January – 31
• February – 28 (29 in a leap year)
• March – 31
• April – 30
• May – 31
• June – 30
• July – 31
• August – 31
• September – 30
• October – 31
• November – 30
• December – 31

The knuckle method: make a fist and count knuckles and valleys. Knuckles (high spots) are 31-day months, valleys (low spots) are 30-day months (February is the exception). Start with the left fist’s index finger knuckle as January, then February valley, March knuckle, and so on. When you reach the pinky knuckle (July), jump back to the index knuckle for August and continue.

Leap Years and February

February has 28 days, but every 4 years it gains an extra day (February 29) in a leap year. The rule for leap years: a year is a leap year if it is divisible by 4, except if it is divisible by 100 (like 1900) unless it is also divisible by 400 (like 2000). This keeps the calendar aligned with the solar year. The next leap years are 2028, 2032, 2036, and so on.

Common Misconceptions

One frequent error is thinking September, October, November, and December are the 7th, 8th, 9th, and 10th months because of their Latin number names. They are actually the 9th through 12th months. Another misconception is that all months have 30 or 31 days except February—true, but the pattern is irregular, so it’s easy to mix up April (30) and May (31) or July (31) and August (31). Also, some people think the year starts in March (as it did in ancient Rome), but in the modern Gregorian calendar, January is always the first month.

How to Remember the Sequence

If you need to recall the order quickly, try these mnemonic devices:

• Rhyme: “Thirty days hath September, April, June, and November; all the rest have thirty-one, except February alone.”
• Knuckle trick (described above).
• Acronym: JFMAMJJASOND (the first letters of each month).
• Group by season: Winter (Dec–Feb), Spring (Mar–May), Summer (Jun–Aug), Fall (Sep–Nov).

Frequently Asked Questions

Why does February have 28 days?

February’s short length comes from the ancient Roman calendar. When the Romans added January and February to the original 10-month year, February was given 28 days to keep the total at 355 days (a lunar year). Later calendar reforms kept it short, and it became the month that absorbs the leap day.

What is the correct order of months in a year?

The order is: January, February, March, April, May, June, July, August, September, October, November, December. This is the standard sequence in the Gregorian calendar, which is the most widely used civil calendar worldwide.

How many days are in each month?

January 31, February 28 (29 in leap years), March 31, April 30, May 31, June 30, July 31, August 31, September 30, October 31, November 30, December 31. The total is 365 days in a common year and 366 in a leap year.

Why do September, October, November, and December have names that mean seven, eight, nine, and ten?

Because in the original Roman calendar, the year began in March, so September was the 7th month, October the 8th, November the 9th, and December the 10th. When January and February were added later, these months shifted to positions 9–12, but their names stayed the same.

What is the difference between a calendar month and a lunar month?

A calendar month is a fixed division of the year (like January or February) with 28–31 days. A lunar month is the time between successive new moons, about 29.5 days. The Gregorian calendar is solar-based, not lunar, so the months don’t align with moon phases.

Is there a month with 32 days?

No. In the Gregorian calendar, the maximum number of days in any month is 31. No month has 32 days, and no calendar system commonly in use today has a 32-day month.

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in m | Month number | - | 1 | 1
out name | Month name | - | lookup(m) | 0