Calendars and Math

A calendar is a math tool that organizes time. It divides the year into months, weeks, and days. People have used calendars for thousands of years to keep track of important dates.

Days, Weeks, and Months

A year has 365 days, or 366 in a leap year. It is divided into 12 months. Each month has 28, 29, 30, or 31 days. A week always has 7 days.

You can use math to figure out what day of the week a date falls on. If today is Monday and an event is in 10 days, you can divide 10 by 7 to find it is a week and 3 extra days, so it falls on Thursday.

Leap Years

A leap year happens every 4 years. February gets an extra day, making it 29 days instead of 28. This keeps the calendar lined up with the Earth's orbit around the Sun.

To check if a year is a leap year, divide it by 4. If it divides evenly, it is usually a leap year. The year 2024 is a leap year because 2024 divided by 4 is 506 with no remainder.

Fun Facts

• The calendar we use today is called the Gregorian calendar. It started in 1582.
• February is the only month that changes its number of days.
• A knuckle trick helps you remember which months have 31 days. The bumps on your knuckles are the long months.

Did You Know?

Every 400 years, the calendar has exactly 97 leap years. This math keeps our calendar accurate to within one day every 3,236 years!