Calendar Basics
The months, the weekdays, and the leap-year rule — where the names come from and how the rule works.
Months of the Year
- 31 days
January
Named for Janus, the Roman god of beginnings.
- 28 days
February
29 days in a leap year — the only variable-length month.
- 31 days
March
Named for Mars; the first month of the old Roman calendar.
- 30 days
April
Possibly from Latin aperire, "to open" (as buds do).
- 31 days
May
Named for Maia, Roman goddess of growth.
- 30 days
June
Named for Juno, queen of the Roman gods.
- 31 days
July
Named for Julius Caesar in 44 BCE.
- 31 days
August
Named for Emperor Augustus in 8 BCE.
- 30 days
September
From septem, "seven" — the 7th month in the old calendar.
- 31 days
October
From octo, "eight" — the 8th month in the old calendar.
- 30 days
November
From novem, "nine" — the 9th month in the old calendar.
- 31 days
December
From decem, "ten" — the 10th month in the old calendar.
Days of the Week
- Day 1
Sunday
Named for the Sun.
- Day 2
Monday
Named for the Moon.
- Day 3
Tuesday
Named for Tiw (Old English) / Mars.
- Day 4
Wednesday
Named for Woden (Old English) / Mercury.
- Day 5
Thursday
Named for Thor / Jupiter.
- Day 6
Friday
Named for Frigg / Venus.
- Day 7
Saturday
Named for Saturn.
About Leap Years
A year is a leap year if it's divisible by 4 — except years divisible by 100, unless they're also divisible by 400. That extra rule keeps the calendar in step with Earth's orbit, which takes a little less than 365.25 days. 2000 was a leap year; 1900 and 2100 are not.
2026 is not a leap year
February has 28 days.