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Measurement · Lesson 9 of 16

Calendars, Days and Months

A calendar shows the days of a month in rows of seven. Knowing the days, months and a few facts about them lets you find any date.

What you will learn

  • Name the days of the week and the months of the year in order.
  • Say how many days are in each month.
  • Read a calendar page and find a date a week or more later.

Before you start: you should be able to count to 3131. Skip Counting in 2s, 5s and 10s can help with counting in sevens too.

The idea

A calendar is a chart of days. It helps us plan birthdays, holidays and school terms. A day is one turn of the Earth. We group days into weeks, weeks into months and months into a year.

Days of the week

There are 77 days in a week, always in the same order: Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday. After Sunday the week starts again with Monday. Different countries start the week on different days, and the calendars on this site start on Monday.

Months of the year

There are 1212 months in a year: January, February, March, April, May, June, July, August, September, October, November, December.

Months have different numbers of days.

Sorted into groups: 31 days, 30 days, Fewer31 days: January, March, May, July, August, October, December. 30 days: April, June, September, November. Fewer: February.31 daysJanuaryMarchMayJulyAugustOctoberDecember30 daysAprilJuneSeptemberNovemberFewerFebruary
Months sorted by length. February has 28 days, or 29 in a leap year.

A year has 365365 days. Roughly every four years, February gets an extra day, 2929 February, and that year has 366366 days. It is called a leap year. The year 20282028 is a leap year.

Reading a calendar page

A calendar page shows one month. Each row is a week, and each column is a day of the week. The number in each box is the date.

Calendar for November 2026November 2026 has 30 days. The 1st is a Sunday, and the weeks start on Monday. Shaded dates: 10.November 2026MonTueWedThuFriSatSun123456789101112131415161718192021222324252627282930
November 2026. The 1st falls on a Sunday. The 10th, shaded, is a Tuesday: it is in the Tuesday column.

To find the day of a date, look at which column its box is in.

Counting forward

Dates in the same column are exactly 77 days apart, because a week is 77 days. So the same weekday comes round every 77 days. On the calendar above, the 11st, 88th, 1515th, 2222nd and 2929th are all Sundays.

To find a date a week later, add 77. To find a date two weeks later, add 1414.

Worked examples

Example 1: What day is it?

On the calendar for November 20262026, what day of the week is the 1515th?

  1. The 11st is a Sunday.
  2. 15−1=1415 - 1 = 14 days later is exactly two weeks later.
  3. Two weeks later is the same day of the week.

Answer: Sunday.

Example 2: Date a week later

A school trip is on Wednesday 1212 March. What is the date of the same day the next week?

  1. A week is 77 days.
  2. 12+7=1912 + 7 = 19.

Answer: Wednesday 1919 March.

Example 3: Crossing into the next month

Today is the 2828th of April. What is the date 55 days later?

  1. Count on from 2828: 2929, 3030.
  2. April has 3030 days, so the next day is 11 May.
  3. Count the remaining days: 11, 22, 33 May.
  4. That is 22 days in April and 33 in May: 55 days.

Answer: 33 May.

“Thirty days has September, April, June and November” is a rhyme that helps you remember which months have 3030 days. All the others have 3131, except February.

Why it matters

Calendars help us plan ahead and work out how long until something. How many days until your birthday? What day is the party? Which month comes after next? Being able to count days and weeks is the first step towards working out durations and timetables, which you will meet in Time and Clocks.

Practice

Your turn. Type or choose an answer, then press Check. Getting one wrong is fine, that is what practice is for. You can try as many times as you like.

Question 1 of 8

How many days are there in one week?

Question 2 of 8

How many months are there in a year?

Question 3 of 8

Which of these months has 3030 days?

Choose one answer

Question 4 of 8

On the calendar for November 20262026, the 11st is a Sunday. What day is the 22nd?

Choose one answer

Question 5 of 8

Today is the 1010th of the month. What is the date exactly one week later?

Question 6 of 8

How many days are there in a leap year?

Question 7 of 8

Which month has the fewest days?

Choose one answer

Question 8 of 8

Which day comes straight after Saturday?