Reference of the 12 months with days, abbreviations, seasons, and quarters.
| # | Month | Abbr. | Days | Season | Quarter |
|---|
About the 12 months
Origin of the month names (Latin roots)
- January — from Latin Ianuarius, named after Janus, the two-faced god of beginnings and transitions.
- February — from Februarius, a Roman purification festival (februa).
- March — from Martius, named after Mars, god of war. Originally the first month of the Roman calendar.
- April — from Aprilis, possibly from aperire («to open»), referring to spring buds.
- May — from Maius, linked to the goddess Maia, nurturer of growth.
- June — from Iunius, named after Juno, queen of the Roman gods.
- July — originally Quintilis (fifth month); renamed in 44 BCE after Julius Caesar.
- August — originally Sextilis (sixth month); renamed in 8 BCE after Emperor Augustus.
- September — from septem (seven), the seventh month in the early Roman calendar.
- October — from octo (eight).
- November — from novem (nine).
- December — from decem (ten). The mismatch between the name and current position (12th) is a relic of the old 10-month Roman calendar that began in March.
Why February has 28 or 29 days
The Roman calendar originally had 10 months starting in March, with winter left uncounted. Around 713 BCE, King Numa Pompilius added January and February. Because the Romans considered even numbers unlucky, he gave most months 29 or 31 days — but the math required one short month, so February got 28. When Julius Caesar reformed the calendar in 45 BCE, he redistributed days to create the 365-day solar year we know, but left February as the short month that absorbs the leap-day adjustment every four years.
The leap-year rule
A year is a leap year (February has 29 days) if:
- It is divisible by 4, and
- It is not divisible by 100, unless
- It is also divisible by 400.
Examples: 2024 → leap (÷4, not ÷100). 2100 → common (÷100 but not ÷400). 2000 → leap (÷400). The rule keeps the calendar year aligned with the solar year of ~365.2422 days, drifting less than one day every 3,000 years.
Frequently asked questions
Why does a year have 12 months?
The 12-month division comes from lunar cycles: a lunar month is roughly 29.5 days, and 12 such cycles (~354 days) approximate a solar year. The Romans standardized the number at 12 around 700 BCE, and the Julian and later Gregorian reforms preserved it while fixing month lengths to match the 365-day solar year. The number 12 also divides cleanly into 2, 3, 4 and 6, which is convenient for quarters, halves, and thirds — hence 4 quarters of 3 months each.
How many days are in each month?
- 31 days: January, March, May, July, August, October, December (7 months)
- 30 days: April, June, September, November (4 months)
- 28 or 29 days: February (1 month — 29 in a leap year)
A memory aid: «Thirty days hath September, April, June, and November. All the rest have thirty-one, except February alone, which has twenty-eight days clear — and twenty-nine in each leap year.» Or the knuckle method: knuckles are 31-day months, dips are shorter ones.
Which months have 31 days?
Seven months have 31 days: January, March, May, July, August, October, and December. Notice that July and August are back-to-back 31-day months — a quirk dating from Augustus supposedly taking a day from February so his namesake month would not be shorter than Caesar's July. Modern historians dispute that story, but the layout survived.
What is a quarter and how do quarters map to months?
A quarter is a three-month segment used in finance, accounting, and reporting. Calendar quarters are:
- Q1: January, February, March
- Q2: April, May, June
- Q3: July, August, September
- Q4: October, November, December
Fiscal years can shift quarters — a fiscal year starting in April makes April–June the first fiscal quarter. This table uses standard calendar quarters.
How do seasons differ between hemispheres?
Seasons are flipped across the equator because Earth's axial tilt points each hemisphere toward or away from the sun at opposite times. When it is winter in New York (Northern Hemisphere, December–February), it is summer in Sydney (Southern Hemisphere). Use the toggle above the table to switch the Season column. Meteorologists commonly group seasons by full months (Dec–Feb winter in the North), while astronomers tie them to solstices and equinoxes (around the 20th–22nd of those months).
A reference widget for the 12 months of the Gregorian calendar. The interactive table lists each month by number, full name, 3-letter abbreviation, number of days, meteorological season, and calendar quarter. Enter any year to see whether February has 28 or 29 days — the leap-year rule is applied automatically (divisible by 4, except century years not divisible by 400). A hemisphere toggle flips the Season column between Northern (December–February = Winter) and Southern (June–August = Winter). Example rows: 01 January / Jan / 31 / Winter / Q1. 02 February / Feb / 28 or 29 / Winter / Q1. 08 August / Aug / 31 / Summer / Q3. Click Highlight current month to locate today. Copy-table button exports a plain-text version.