How to Calculate Days, Weeks, Months, and Years in Maths
Days
The theory of day and night goes back to our Simian predecessor. You might be surprised to know that the Indo-European week was of 9 days (a 3rd of a month). This is why in so many languages the term for “nine” and “new” is so plainly related. The days of the week were named by the Babylonians (ancient Akkadian-speaking state in central-southern Mesopotamia) after the Sun, the Moon and the five known planets. Germanic nations named the days in their 7 day week.
Days of The Week
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
Sunday
Saturday and Sunday are considered as the weekend and thus fall at the termination of the week.
Week
A week is basically a breakdown of a monthly cycle of 29.5 days into 4 intervals of 7 days each; using leap days to remain in sync with the moon phases in the long-run. It is an easy way to constitute all phases of the moon as it completes a full orbit everywhere about the earth. It takes a period of about 15 days from new moon to the full moon, as seen from earth. A month (4 weeks) is equal to about 2 cycles of the new moon to new moon.
Month
A month is a breakdown of the year into 12 cycles = about 29.5 days = around the interval for the moon to complete a full orbit of the earth (the actual cycle is of approximately 27.3 days, which is why we have leap days to consider for the variance).
If you have observed months do not fit clearly into years. This is to say each month does not hold equal days. The Babylonians had an opinion that 360 accounts for a number of prime factors that it was a number apt for a heavenly body, but a 7 day week did not fit clearly into this. Julius Caesar’s calendar reform in 46 BC got around this by months which substituted between 30 and 31 days. His nephew Augustus did not like having a birth month of only 30 particularly as his uncle’s July had 31 days so he disturbed things by doing out February of a day to make up for the difference.
As already mentioned, a year is divided into 12 months. A month either has 30 days or 31 days (except February having 28 days and 29 in a leap year). Following is the cycle of months:
Months of The Year
Year
The year is an approximate breakdown into 365 days = the interval for the earth to fully achieve a full orbit of the sun.
Seasons of The Year
Summer
Winter
Spring
Autumn/fall
Fall is the term used in the United States, whereas autumn is used elsewhere in the world.
Solved Examples
Example:
Calculate the number of days in a year.
Solution:
for the purpose of finding the number of days in a year we would require to calculate:
[7 × 31] + [4 × 30] + [1 × 28]
= 217 + 120 + 28
= 365
For leap year
[7 × 31] + [4 × 30] + [1 × 29]
= 217 + 120 + 29
= 366
Example:
Find out the next leap year that comes after 2000.
Solution:
We are already familiar that,
1 week = 7 days.
Now in order to determine the number of weeks in a year, we are required to divide 365 by 7.
Thus, 365 ÷ 7 = 52 weeks and 1 day
We can learn from the calendar that
7 days = 1 week
Approximately 52 weeks = 1 year
12 months = 1 year
365 days = 1 year
366 days = 1 leap year
Approximately 4 weeks = 1 month
10 years create one decade.
100 years create one century.
1000 years create one millennium.
Fun Facts
The days of the week, months of the year in English always begin with CAPITAL letters. For example:
February correct - february incorrect.
Wednesday correct - wednesday incorrect.
The first letter of the seasons does not start with capital letters.
FAQs on Days, Weeks, Months, and Years Explained
1. How many days, weeks, and months are there in a year according to the 2025-26 calendar?
According to the standard Gregorian calendar used in the CBSE curriculum for 2025-26, a standard year has 365 days, which are grouped into 12 months. These 365 days also make up 52 full weeks plus one extra day.
2. What is a leap year and why is it important?
A leap year is a year that has 366 days instead of the usual 365. This extra day is added to keep our calendar aligned with the Earth's journey around the sun. It occurs every four years, and the extra day is added to February, making it 29 days long. Understanding leap years is important for accurately calculating dates over long periods.
3. Which months of the year have 31 days?
The months that have exactly 31 days are:
January
March
May
July
August
October
December
A simple way to remember this is the 'knuckle trick'.
4. How many days are in a week and what are they called?
There are seven days in a week. As per the NCERT syllabus, it's important to know them in order. They are: Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, and Saturday.
5. How can you calculate the number of weeks in a certain number of days?
To calculate the number of weeks for a given number of days, you simply divide the total number of days by 7. For example, to find the number of weeks in 28 days, you calculate 28 ÷ 7, which equals 4. So, there are exactly 4 weeks in 28 days.
6. Why are there not exactly 4 weeks in every month?
If there were exactly 4 weeks in a month, each month would have 28 days (4 weeks x 7 days). However, all months except for a non-leap year February have more than 28 days (30 or 31). This is because the 12 months must add up to 365 days in a year. This structure helps the calendar align with the seasons and the lunar cycle, even if it means months don't have a perfectly round number of weeks.
7. What is the 'knuckle trick' to remember the number of days in each month?
The knuckle trick is a simple memory aid. Make a fist. The knuckles (the high bumps) and the grooves (the low spaces between them) represent the months.
- Start with your first knuckle as January. It's a high bump, so it has 31 days.
- The next groove is February, which is low and has fewer days (28 or 29).
- The next knuckle is March (31 days), and so on.
Every month that lands on a knuckle has 31 days, and every month on a groove has 30 days (or 28/29 for February).
8. Why is it important to learn about days, weeks, and months in daily life?
Understanding these units of time is a fundamental life skill. It helps us to:
Read a calendar to know the date.
Plan schedules for school, homework, and holidays.
Remember important events like birthdays and festivals.
Understand deadlines and plan for the future.
9. Are 52 weeks exactly equal to one year?
No, 52 weeks are not exactly equal to one year. 52 weeks make up 364 days (52 x 7 = 364). A normal year has 365 days, and a leap year has 366 days. This means a normal year is actually 52 weeks and 1 extra day, and a leap year is 52 weeks and 2 extra days. This is why the day of the week for a particular date, like your birthday, shifts forward by one day each year (or two after a leap day).
