Why February Has 28 or 29 Days, and the Zodiac Sign of Leap-Day Babies

Why February has only 28 days

The answer starts in ancient Rome. Britannica explains that the first Roman calendar had only 10 months, 304 days in all, and that King Numa Pompilius later added January and February to make a year of twelve months.

Numa wanted a lunar year of 355 days, and Roman superstition, Britannica notes, held that even numbers were unlucky. So he took a day off each 30-day month to make it 29. But twelve odd numbers always add up to an even total, so to reach an odd 355 one month had to have an even number of days. He chose February, the month of Roman rituals honouring the dead, and gave it 28 days. Later reforms changed many things about the calendar, but February's 28-day base length has lasted ever since.

Why it sometimes has 29

The problem is the sun. The Earth takes about 365.2422 days to go round the sun, as Australia's Bureau of Meteorology Space Weather Services puts it, so a 365-day calendar slowly drifts away from the seasons, by almost a quarter of a day each year.

Julius Caesar fixed most of that. Wikipedia's article on the Julian calendar explains that he proposed the reform in 46 BC, with the astronomer Sosigenes of Alexandria generally considered its main designer, and that it took effect on 1 January 45 BC. To bring the seasons back into line, 46 BC itself was stretched to 445 days, remembered as the last "year of confusion". From then on, a year had 365 days with one extra day every fourth year, an average of 365.25 days. The extra day went into February: the Romans counted it as a doubled day near the end of the month, just before the start of March.

The leap-year rule today

365.25 days is still a little too long. The Bureau of Meteorology notes that under the Julian calendar the seasons still drifted by a day about every 128 years. By the 16th century the error had grown so large that Pope Gregory XIII reformed the calendar in 1582, and 10 days were left out of October that year.

His rule is the one we still use:

• A year divisible by 4 is a leap year, with 29 February: 2024 and 2028, for example.
• But a year divisible by 100 is not a leap year: 1700, 1800 and 1900 had no 29 February, and 2100 will not have one either.
• Unless it is also divisible by 400: 2000 was a leap year, and so will 2400 be.

The result averages 365.2425 days a year, very close to the real 365.2422.

Born on 29 February

People born on leap day are often called leaplings. New Hampshire Public Radio puts the odds of being born on 29 February at about 1 in 1,461, the number of days in four years. It also quotes an estimate from the Honor Society of Leap Year Day Babies of roughly five million leaplings in the world.

The zodiac surprise: always a Rat, Dragon or Monkey

Here is something that follows from simple arithmetic. Every leap year is divisible by 4, and the Chinese zodiac repeats every 12 years. Since 12 is a multiple of 4, leap years can only ever land on three of the twelve animals, each four years apart: the Rat, the Dragon and the Monkey.

And 29 February always comes after Chinese New Year, which falls between 21 January and 20 February in the table our zodiac checker uses. So everyone born on 29 February belongs to the new year's animal, and that animal is always a Rat, a Dragon or a Monkey. Those three also happen to form one of the four traditional compatibility triangles, which makes leap-day babies a natural match for each other. Our Rat and Dragon compatibility guide explains what the triangle means.

These are the recent leap years and the zodiac sign of a 29 February birthday in each:

• 1948: Earth Rat
• 1952: Water Dragon
• 1956: Fire Monkey
• 1960: Metal Rat
• 1964: Wood Dragon
• 1968: Earth Monkey
• 1972: Water Rat
• 1976: Fire Dragon
• 1980: Metal Monkey
• 1984: Wood Rat
• 1988: Earth Dragon
• 1992: Water Monkey
• 1996: Fire Rat
• 2000: Metal Dragon
• 2004: Wood Monkey
• 2008: Earth Rat
• 2012: Water Dragon
• 2016: Fire Monkey
• 2020: Metal Rat
• 2024: Wood Dragon
• 2028: Earth Monkey

The next leap day, 29 February 2028, falls in a Monkey year: Chinese New Year 2028 is on 26 January. The same is true of 28 February: it always comes after Chinese New Year, so a 28 February birthday also always belongs to the new year's animal. Only January and early-February birthdays need checking, as our guide Born in January? explains.

Leap months in the Khmer calendar

The Khmer lunar calendar solves the same problem in a different way. Twelve moons make only about 354 days, so instead of a single leap day it sometimes adds a whole second month of Asadh, and sometimes one extra day to the month of Jesth. 2026 was one of those leap-month years. Our guide to Khmer leap months and leap days explains how it works, and the Khmer Calendar shows the lunar date for any day.

Frequently asked questions

Why does February have 28 days?

Because the Roman king Numa Pompilius, when he added January and February to the calendar, needed one month with an even number of days to make a 355-day year, and chose February.

Why is there a 29 February?

The Earth takes about 365.2422 days to go round the sun. Adding a day every fourth year, as Julius Caesar's calendar did from 45 BC, keeps the calendar in step with the seasons.

Is 2100 a leap year?

No. Years divisible by 100 are not leap years unless they are also divisible by 400. 2000 was a leap year; 2100 will not be.

What is the Chinese zodiac sign of someone born on 29 February?

Always a Rat, a Dragon or a Monkey, because leap years are divisible by 4 and the zodiac repeats every 12 years. For example, 29 February 2024 fell in a Dragon year, and 29 February 2028 will fall in a Monkey year.

When is the next 29 February?

29 February 2028.

Sources and further reading

• Britannica: “Why Are There Only 28 Days in February?” — the ten-month Roman calendar, Numa Pompilius adding January and February, the superstition about even numbers and the 355-day year.
• Wikipedia: “Julian calendar” — Caesar's reform proposed in 46 BC and in effect from 1 January 45 BC, Sosigenes of Alexandria, the 445-day year and the 365.25-day average.
• Bureau of Meteorology, Space Weather Services: “Leap years” — the 365.2422-day year, the Julian drift of one day in about 128 years, the 1582 reform with 10 days left out of October, and the divisible-by-4, 100 and 400 rule.
• New Hampshire Public Radio: “Stuff You Probably Didn't Know About Leap Day” (29 February 2016) — the 1 in 1,461 odds of a leap-day birthday, the estimate of about five million leaplings, and Pope Gregory XIII's reform.
• Farmers' Almanac: “When Is Lunar New Year 2027?” — Lunar New Year falls between 21 January and 21 February.

Calendar history follows the sources listed above. Zodiac signs follow the Lunar New Year table used by our zodiac checker; the zodiac is shared as culture, not as a prediction.