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Maths Facts

Why calendars are tricky

Explore months with different lengths and leap years.

Quick answer

Calendars are tricky because months have different numbers of days, and every four years we have a leap year with an extra day.

Learning outcome

By the end of this page, you will understand why calendars have different numbers of days in each month and how leap years work. Success signs:
  • You can name the months with 30 or 31 days
  • You know what a leap year is and why we have one
  • You can explain why calendars are different from each other
  • You can count how many days are in a year

Why this matters

Calendars help us keep track of time, plan our days, and know when special events happen. Understanding how calendars work helps you know when birthdays, holidays, and school events are coming. It also helps you understand why some years are longer than others and how we keep our calendar system in sync with Earth's orbit around the sun.

How it works

Let's look at how calendars are built:
  1. There are 12 months in a year
  2. Each month has a different number of days
  3. Some months have 30 days, some have 31, and one has 28 or 29
  4. Every four years, we add an extra day to February
  5. This extra day makes a leap year

Examples you can see

Let's look at how many days are in each month: Days in each month
Month Number of Days
January 31
February 28 (29 in leap years)
March 31
April 30
May 31
June 30
July 31
August 31
September 30
October 31
November 30
December 31
Let's try to count how many days are in a whole year:
  • January: 31 days
  • February: 28 days
  • March: 31 days
  • April: 30 days
  • May: 31 days
  • June: 30 days
  • July: 31 days
  • August: 31 days
  • September: 30 days
  • October: 31 days
  • November: 30 days
  • December: 31 days
Now let's add them up: 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 + 31 = 365 days That's a whole year!

Try it as a mini adventure

Let's go on a calendar adventure! Adventure: The Calendar Detective You are a detective trying to solve why calendars are so confusing. You have a puzzle to solve.
  1. First time: Count how many days are in the first three months (January, February, March)
  2. Second time: Find out how many days are in the last three months (October, November, December)
  3. Third time: What is the total number of days in all the months that have 30 days?
  4. Fourth time: How many days are in all the months that have 31 days?
  5. Fifth time: What is the difference between the longest and shortest months?
Let's work it out together:
  1. January: 31 days, February: 28 days, March: 31 days = 90 days total
  2. October: 31 days, November: 30 days, December: 31 days = 92 days total
  3. Months with 30 days: April, June, September, November = 4 months × 30 = 120 days
  4. Months with 31 days: January, March, May, July, August, October, December = 7 months × 31 = 217 days
  5. Longest month: 31 days, Shortest month: 28 days = 31 - 28 = 3 days difference

Common mistakes

  • Mistake: Thinking all months have the same number of days.
    Why it happens: Children often don't notice the pattern or don't know how many days each month has.
    Fix: Use a calendar or write down the months and their days to see the pattern.
  • Mistake: Forgetting that February has 28 days (or 29 in a leap year).
    Why it happens: February is the shortest month, so it's easy to forget its number of days.
    Fix: Remember the rhyme: "Thirty days hath September, April, June, and November. All the rest have thirty-one, except February, which has twenty-eight, and twenty-nine in leap years."
  • Mistake: Confusing leap years with regular years.
    Why it happens: Leap years only happen every four years, so children don't see the pattern.
    Fix: Mark leap years on a calendar or use a chart to show when they happen.

Parent and carer guide

  1. Help your child remember the number of days in each month by using a rhyme or song.
  2. Use a real calendar to count the days together.
  3. Explain that leap years are a way to keep our calendar in sync with Earth's orbit.
  4. Point out that the extra day in February is added to keep the seasons aligned with the calendar.
  5. Ask questions like: "Which month has the most days?" or "How many days are in a year?"
  6. Encourage your child to look for patterns in the months.
  7. Let them make a chart or poster showing the months and their days.
  8. Use games or puzzles to reinforce learning.
  9. Be patient if they get confused – it's normal to need time to understand calendars.
  10. Remember to celebrate their progress when they get it right!

Practice questions

  1. How many days are in a leap year?
  2. Which month has 28 days?
  3. How many months have 30 days?
  4. How many days are in the first six months of the year?
  5. What is the total number of days in all the months that have 31 days?
Answers:
  1. 366 days
  2. February
  3. 4 months (April, June, September, November)
  4. January: 31, February: 28, March: 31, April: 30, May: 31, June: 30 = 181 days
  5. 7 months × 31 days = 217 days

FAQ

Why do we have leap years?

Leap years happen because Earth takes about 365.25 days to orbit the sun. We add an extra day every four years to keep our calendar in sync with the seasons.

How many days are in a leap year?

A leap year has 366 days. The extra day is added to February, making it 29 days long instead of 28.

Why do some months have 30 days and others have 31?

This is based on ancient Roman calendar systems. The months were designed to align with the phases of the moon and to fit the number of days in a year.

When was the last leap year?

The last leap year was 2024. The next leap year will be 2028.

Can you make a chart of all the months?

Yes! You can write each month and its number of days to help remember. You can also use a calendar to see how the days are arranged.