Thirty-one. That’s the short answer. If you just needed to settle a bet or double-check your wall calendar, there you go—January has 31 days. Every single year.
But honestly, the "why" behind those 31 days is a mess of ancient superstitions, ego-driven Roman politics, and a literal "year of confusion" that lasted 445 days. Most of us just flip the calendar page and don't think twice about it, but the reason January isn't 30 days or 28 days like its neighbor February is actually kind of wild.
How Many Days Does Jan Have and Who Decided That?
Back in the day—we’re talking 700s BCE—the original Roman calendar was a total disaster. It only had ten months. It started in March (Martius) and ended in December. If you’re doing the math, that only accounts for about 304 days. The Romans basically just ignored winter. They treated it as a "month-less" gap where nothing much happened because you couldn't farm.
Eventually, a king named Numa Pompilius realized this was a terrible way to run an empire. He added January and February to the end of the year to bridge the gap.
Here is where it gets weird: the Romans were terrified of even numbers. They thought they were unlucky. Numa wanted the year to have 355 days (a lunar year), so he made most months 29 or 31 days. But since you can't have an odd total year by only adding odd numbers, one month had to be the "unlucky" even one. He chose February, giving it 28 days, and designated it as a time for purification and mourning.
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January, meanwhile, was given 29 days. It stayed that way for centuries.
The Julius Caesar Glow-Up
By the time Julius Caesar came around, the calendar was completely out of sync with the seasons. Imagine celebrating a harvest festival in the middle of spring. That was the reality.
In 46 BCE, Caesar got fed up. He consulted an astronomer named Sosigenes of Alexandria. They ditched the lunar cycle and moved to a solar-based system (the Julian Calendar). To make the numbers work for a 365-day year, Caesar tacked on extra days to several months. January was bumped from 29 days up to 31.
He also moved the start of the year from March to January 1st. Why? Because January was named after Janus, the god of doors, gates, and beginnings. Janus has two faces—one looking back at the past and one looking forward to the future. It’s pretty poetic, even if it was just a way to make taxes and political terms easier to track.
Why January Never Changes (Unlike February)
You've probably noticed that February is the "problem child" of the calendar, jumping between 28 and 29 days. People often ask if January ever loses a day during leap years.
Nope.
January is a "full month." In the Gregorian calendar—which is what we use today—the lengths of the months are fixed to keep the seasons from drifting. If we started messing with January’s 31 days, we’d throw off the entire solar alignment that Pope Gregory XIII fought so hard to fix in 1582.
Surprising Facts About January's Length
- The Perihelion Connection: Around January 4th, Earth is actually at its closest point to the Sun (perihelion). Even though it's winter in the Northern Hemisphere, we're physically nearer to our star than at any other time of the year.
- The "Wolf Moon": Because January has 31 days, it almost always sees a full lunar cycle. The first full moon of the month is traditionally called the Wolf Moon, named by Native American tribes who heard wolves howling in hunger outside their camps.
- Three Months, One Start: In a leap year, January starts on the same day of the week as April and July. If January 1st is a Wednesday in a leap year, April 1st and July 1st will be too.
Misconceptions About the 31 Days
A common myth floating around the internet is that August has 31 days because Augustus Caesar "stole" a day from February to make his month as long as Julius Caesar’s July.
While that makes for a great story about ego, it’s mostly bunk. Records suggest the month lengths were likely already established before Augustus took power. January having 31 days was a purely mathematical decision to ensure the year added up to 365.25 days.
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What You Can Do With This Information
Knowing January has 31 days isn't just for trivia night. It’s the longest month of the year (tied with six others), which is why "Janu-worry" is a real thing. It’s a long time to wait for a paycheck after the holidays.
- Plan your budget for 4.5 weeks: Since January spans five different weeks, your grocery and gas budget needs to stretch further than it does in February.
- Audit your subscriptions: Most "monthly" bills charge the same amount whether the month has 28 or 31 days. In January, you're technically getting the best "value" per day for your Netflix or gym membership.
- Use the "Janus" mindset: Take the first 15 days to reflect on the previous year and the final 16 days to set concrete actions for the new one.
The 31 days of January are a permanent fixture of our modern world. Unless we decide to scrap the Gregorian calendar and move to something like the 13-month "International Fixed Calendar" (where every month is 28 days), you can always count on January 31st being the day you finally take down your Christmas lights.
To make the most of the long stretch in January, audit your recurring expenses on the 31st to ensure your New Year's resolutions are actually reflected in your spending habits. Stay ahead of the "long month" slump by scheduling a mid-month milestone on the 15th to break up the 31-day marathon.