Calendar & Dates Lab

Navigate through months, count weekdays, and discover patterns in how calendars are organized. Do all months work the same way?

Guided Experiment: Calendar Patterns Investigation

Before you start, predict: which months have more Saturdays -- months that start on Saturday, or months that start on Sunday? Write your guess.

Write your hypothesis in the Lab Report panel, then click Next.

Controls

Navigate through months from January 2024 to December 2025. Explore calendar patterns and record data to find out if all months work the same way.

January 2024

Sun
Mon
Tue
Wed
Thu
Fri
Sat
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31

31

Days in Month

Monday

First Day

8

Weekend Days Total

How many of each day?

Sun

4

Mon

5

Tue

5

Wed

5

Thu

4

Fri

4

Sat

4

Things to investigate

  • Which months have 31 days? Which have 30? Which has fewer?
  • Can a month ever have 5 Sundays? What about 5 Saturdays?
  • Does the first day of the month change how many weekends there are?

Data Table

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Reference Guide

Reading a Calendar

A calendar shows all the days in a month arranged in rows by week. Each column is a day of the week, starting with Sunday on the left.

  • Each row is one week (7 days)
  • The first row may not start on Sunday
  • The last row may not end on Saturday
  • The first number shows which day of the week the month begins on
Key idea: the day of the week that the 1st falls on determines the shape of the whole month.

Days and Weeks

There are 7 days in every week. A month has either 28, 29, 30, or 31 days depending on which month it is.

  • 28 or 29 days: February (29 in a leap year)
  • 30 days: April, June, September, November
  • 31 days: January, March, May, July, August, October, December
A leap year happens every 4 years. It adds one extra day to February (the 29th). 2024 is a leap year.

Months of the Year

There are 12 months in a year. Each month has a name and a number of days. The order of months never changes.

1. January (31)

2. February (28/29)

3. March (31)

4. April (30)

5. May (31)

6. June (30)

7. July (31)

8. August (31)

9. September (30)

10. October (31)

11. November (30)

12. December (31)

Calendar Patterns

Every month has either 4 or 5 of each weekday. A month can never have 6 of the same weekday because months are not long enough.

A 31-day month always has 3 days that appear 5 times. A 30-day month has 2 days that appear 5 times. A 28-day February has exactly 4 of every weekday.

  • Standards: 1.MD.3, 2.MD.7
  • Wraps: Calendar and Dates Explorer tool