How Many Weeks in a Year?

Monday, March 16, 2020
Christopher Sirk

How many weeks in a year 

There are 52 weeks in a year, on average. 

If you want to get even more precise, the number is 52.143 weeks. There’s an extra day in the common year. There’s two in a leap year. 

Very good then. Why would anyone care to know how the number of weeks?

For one, there’s the planning aspect. 

It’s easy to float through a year. It’s harder to develop an action plan and realize it. Day by day, week by week, it’s easy to drift and miss goals and deadlines.

When planning for work, it’s important to manage time. And to develop objectives that can be met within this time. So that you work hard, and at the end of the year you feel accomplished. 

Consider the influential psychologist Edwin Locke. His theory of task motivation states that “conscious ideas regulate [one’s] action.” 

As a result, one needs to clarify focus and define goals. Step one is delineating how much time you have to get things done. 

How many weeks in a year 2021

In 2021, there are 52 weeks. 

Technically there are 52 weeks in full and 2 extra days. But if we go by week numbers according to the week start date, there’s 53. 

This is the system used by the International Organization for Standardization (ISO). ISO 8601 is the name of the organization’s standardized global calendar. It’s meant to be unambiguous and make it easy to label specific dates for communication and posterity. 

Weeks in a year calculation

Don’t worry, this won’t require any CALC 101 skills.

As said, on average there’s fifty-two weeks in a year. But if you do the math, you will find that 52weeks x 7 days = 364. One day is missing. 

Of course, we can count weeks like we count days. Just take 365 or 366 days and divide it by 7. That will give you the number of weeks with some decimal points. You can just round down from there.

Then there’s the ISO system. In ISO 8601, weeks are numbered from W01 to W53. 

We all know the new year starts on January 1. But the first day of the year doesn’t often coincide with a new week. The first week of the year usually begins the previous year.

An ISO week date can start in the previous year. Or end in the next year. 

Here’s how the numbering system works. We’ll use 2021 as an example.

The first week of 2021 is Week 1. It starts December 28, 2020. It ends on January 5, 2020. 

The last week of 2021 is Week 52. It starts December 27, 2021. It ends on January 3, 2021. 

So the first and last week of the year sits between two years. According to ISO this is fair game.

ISO system states it’s permissible to have up to 3 days in the previous year’s calendar.  December 28 is the last day a week can start in a given year. So for example, if a week starts December 29, it will labelled as W01 of the next year.

A note about leap years

Leap days always take place in February. That’s why February 29th is a special day. It only takes place every 4 years.

How many working weeks in a year

Technically, all the average full year’s 52 weeks are fair game for work. 

In practice, 48 working weeks a year is the average. At least in the United States.

Here’s how that calculation was made.

In the US, there are 10 federal holidays. If they don’t fall on weekdays, they are always carried forward or back. So the average person should get 10 days off.

In other words, you can block off two weeks of the year as non-work weeks. 

Then there’s paid leave. 

The average rate is 10 days a year for private sector employees with over 1 year of experience. It’s 15 days a year for workers with 5 to 10 years of experience. And it grows steadily from there.

So add at least 2 more weeks to the “non-work” category. 

And there we have it, an average of 48 working weeks a year.

How many weekdays in a year

On average, there are 261 weekdays in a year. 

There are 262 weekdays in 2021. The number of weekdays in 2021, by specific day, is as follows:

  • Mondays - 52

  • Tuesdays - 52

  • Wednesdays - 52

  • Thursdays - 52

  • Fridays - 52

In the United States, there are 252 working days in 2021.

How many weeks in a month

The average number of weeks in a month is 4.345.

Each month has at least 4 full weeks. But as we all know, some months have 1, 2, or 3 days extra.

Below are the number of days per month. Note February is the odd month out. It has 28 or 29 days, depending on the calendar year.



has 31 days. 4 weeks + 3 days.


has 28 days in the common year, and 29 in a leap year. 4 weeks or 4 weeks + 1 day.


has 31 days. 4 weeks + 3 days.


has 30 days. 4 weeks + 2 days.


has 31 days. 4 weeks + 3 days.


has 30 days. 4 weeks + 2 days.


has 31 days. 4 weeks + 3 days.


has 31 days. 4 weeks + 3 days.


has 30 days. 4 weeks + 2 days.


has 31 days. 4 weeks + 3 days.


has 30 days. 4 weeks + 2 days.


has 31 days. 4 weeks + 3 days.


How many days in a year

The normal year has 365 days. A leap year has 366 days. 

Calendars use fractions to approximate the earth’s orbit around the sun. Leap years are added to correct the measurement of time every 4 years. 

That’s because the true length of a year on earth is fractional. According to NASA, it’s 365.2422. We round that to 365.25. 

0.25 x 4 = 1. So we can see that after 4 years, we have an extra day we need to add. 

A bit more about fractions. The Julian and Gregorian calendars both have 365 days. But their fractional calculations result in an annual 11 minute time difference.

In practice, that means the Gregorian calendar results in 3 fewer days for every 400 years. This accounts for the differences in dates between the two in historical records.

The Julian calendar was dominant in Europe and European colonies until 1582. Then the Gregorian calendar took over. We’ve continued using it to this day.

But old habits die hard. Some parts of the Eastern Orthodox and Oriental Orthodox churches still use the Julian calendar.