Why does a year have 12 months, and why are they named the way they are? The answers go back to ancient Rome — to the Moon, to gods and emperors, and to a counting system that left four months with the "wrong" names. Here's the story behind January to December.
For the modern calendar, see the Gregorian calendar, or browse any month from January.
Why 12 months?
The number 12 comes from the Moon. Early calendars counted lunar cycles — and there are roughly 12 lunar months (each ~29.5 days) in a solar year. The Romans formalised a 12-month year, and the Gregorian calendar kept it, fixing the month lengths so they total 365 (or 366) days.
Fun fact: the earliest Roman calendar had only 10 months and began in March — winter was an unnamed "dead" period. January and February were added later.
Where the month names come from
| Month | Origin of the name |
|---|---|
| January | Janus, Roman god of beginnings and doorways |
| February | Februa, a Roman purification festival |
| March | Mars, the god of war (the old year's start) |
| April | Possibly Aphrodite, or Latin aperire ("to open" — spring buds) |
| May | Maia, a goddess of growth |
| June | Juno, queen of the Roman gods |
| July | Julius Caesar (renamed from "Quintilis") |
| August | Emperor Augustus (renamed from "Sextilis") |
| September | Latin septem = seven |
| October | Latin octo = eight |
| November | Latin novem = nine |
| December | Latin decem = ten |
The "wrong number" mystery
Notice that September–December are named for 7, 8, 9 and 10 — yet they're the 9th to 12th months. Why?
Because the original Roman year began in March. Back then, September really was the seventh month. When the year-start moved to January (set by Julius Caesar in 45 BC), the names stuck — leaving them permanently two off. It's a 2,000-year-old fossil hiding in plain sight on every calendar.
July and August: named for two rulers
- July was renamed from Quintilis ("fifth") to honour Julius Caesar, who was born in that month and reformed the calendar.
- August was renamed from Sextilis ("sixth") for Augustus, the first Roman emperor — and, legend says, lengthened to 31 days so it wouldn't be "shorter" than Caesar's July.
Quick answers
Why are there 12 months in a year? Because there are roughly 12 lunar cycles in a solar year — the Romans formalised a 12-month calendar that we still use.
Why are September to December named after 7–10? The original Roman year began in March, so they were once the 7th–10th months. The names stuck after January became the new start.
Which months are named after people? July (Julius Caesar) and August (Emperor Augustus). The rest come from Roman gods, festivals or numbers.
What was the original first month? March. The earliest Roman calendar had 10 months and started in spring; January and February were added later.