# How many weeks in a year?

Mariana Holostenco  June 28, 2021

## Most often the answer to the question "How many weeks are in a year" is 52.

A simple mathematical calculation contradicts this number of 52.

Specifically, we know that in a common year there are 365 days. If we divide this number by 7 days in a week, we will see that it gives us a result with decimals. Exactly 52,143. That means 52 weeks and one more 1 day.

Common year
365 days in a year / 7 days in a week = 52.143 weeks in a year

The same thing happens in a Leap year. In this type of year we have 366 days. If we divide 366 by 7 days of a week, the result is 52,286. That is 52 weeks and 2 more days.

Leap year
366 days in a year / 7 days in a week = 52.286 weeks in a year

But returning to the question "How many weeks are there in a year?", 52 is the correct answer because this is the established and generally accepted convention.

In turn, the 7-day week is also just a convention, a standard time period. It has nothing to do with anyone or anything, that's just how it was established.

## Astral events from which day, month and year are derived

In fact, the duration of all these intervals, Day, Month and Year, are conventions established on the basis of standardized approximations. But, unlike the fact that the week has 7 days, which is simply established as a convention, the day, the month and the year are really based on the duration of certain events. Thus:

### The day

Has 24 hours and represents the time interval in which the earth makes a complete rotation around its own axis.
But, in relation to the stars, the earth rotates once every 23 hours, 56 minutes and 4 seconds. Therefore, the 24-hour interval was accepted for standardization.

### The month

Is the time interval in which the Moon makes a complete orbit around the Earth. In reality, this move happens in 27.3 days, but the convention is:

• 30 days for April, June, September, and November
• 31 days for January, March, May, July, August, October, and December
• 28 days for February in a Common year
• 29 days for February in a Leap year

### The year

Is the time interval in which the Earth makes a complete rotation around the Sun.
This happens over 365 days, 6 hours, and 9 minutes. The convention is to consider that 3 years have 365 days and every fourth has 366.

## Common year vs. Leap year

The Solar year represents the time interval in which the Earth makes a complete rotation around the Sun. As we have seen, this happens in 365.25 days. Precisely for this reason:

The Common years are those in which it has been established that 365 days will be considered, and the difference of 0.25 will always be added to the fourth year.

The Leap year is called this fourth year to which is added the remaining 0.25 days from the previous 3 years. Therefore, it will have 366 days.

### How to recognize a Leap year

When we have in front of us the calendar of the year that interests us, we can find out very easily if that year is a Common or a Leap one. This is because in a Leap Year February will be 29 days, unlike the Common years when it has only 28.

But what if we don't have a calendar to identify how many days February has?

In this situation we can take into account the fact that a leap year will meet the following three conditions:

1. A Leap year is evenly divisible by 4. Regardless of the number, the result must be an integer number. That means they shouldn't have decimal places
2. But, if it is evenly divisible by 100, then is NOT a Leap Year
3. But, if it is evenly divisible by 400, then is NOT a Leap Year

### How to calculate if a certain year is a Common or Leap one

We take for example the years 2021, 1992, 2000, and 1900, and apply the calculation formula in three steps:

#### Step 1

Divide the year by 4. If it is evenly divisible then go to Step 2; If not, then it is a Common year.

2021 / 4 = 505.25 => Common Year (365 days -> 52 weeks + 1 day)
1992 / 4 = 470.00 => Step 2
2000 / 4 = 500.00 => Step 2
1900 / 4 = 475.00 => Step 2

As we see from these calculations:

• The year 2021 it’s not evenly divisible by 4, therefore it is a Common year (not Leap). This year has 365 days and this means 52 weeks and 1 day.
• Instead, the years 1992, 2000, and 1900 are evenly divisible, so we will have to move on to Step 2

#### Step 2

Divide the year by 100. If it is evenly divisible then go to Step 3; If not, then it is a Leap year.

1992 / 100 = 19.92 => Leap year (366 days -> 52weeks +2days)
2000 / 100 = 20.00 => Step 3
1900 / 100 = 19.00 => Step 3

Here we can see that:

• The year 1992 it’s not evenly divisible by 100, although it was evenly divisible by four, which means it’s Leap year. It means that it has 52 weeks and 2 days, which means 366 days.
• The years 2000 and 1900, are evenly divisible by 100, as they were by 4, so we move on to Step 3

#### Step 3

Divide the year by 400. If it is evenly divisible then it is a Leap year; If not, then it is a Common year.

2000 / 400 = 5.00 => Leap year(366 days -> 52weeks +2days)
1900 / 400 = 4.75=> Common year(365 days -> 52 weeks + 1 day)

From this last step we obtain the following situations:

• The year 2000 is evenly divisible by 400, like it also was by 4 and 100. Therefore, it is a Leap year, and it has 366 days (52 weeks + 2 days).
• The year 1900 it’s not evenly divisible by 400, even though it was by 4 and 100. Therefore, it is a Common year, and it has 365 days (52 weeks + 1 day).

### Name and order of the days of the week

In different cultures, the names of the days of the week derive from the names of some planets or deities and their order may be different.
For example, while in most of Europe the week begins on Monday, in the United States or Japan the first day of the week is considered to be Sunday.

• Sunday, derived from the Old English “Sunnandæg” , is named after the Sun. Depending on the area it can be considered the last or the first day of the week. Usually it is considered a rest day.
• Monday, or day of the moon, derived from Old English Mōnandægis is named after the Moon. It can be considered the first or the second day of the week.
• Tuesday, or Tiw’s day (the god of single combat, and law and justice in Norse mythology) derived from Old English Tiwesdægis. In other cultures, it is named after planet Mars or the Roman God of war.
• Wednesday, derived from Old English Wōdnesdæg, is named after the planet Mercury, or the Roman God.
• Thursday is named after Thor, the Norse god of Thunder, or the planet Jupiter, or Zeus (Jove), the supreme Roman God.
• Friday, or the “day of Frig” (the Germanic goddess), or after planet Venus, or the Roman goddess of love and beauty.
• Saturday is named after the planet Saturn, or the Roman god of agriculture. It is considered a weekend day, together with Sunday.

### What is the origin of the 7-day week?

Although it does not match the months or solar year, the week has 7 days. It seems that the Babylonians are the ones who set the 7-day week. It is interesting that, despite the inadvertencies with the astral events, these 7 days have remained the same until today. And just as interesting is that, from time to time, there are still attempts to change this number.

There are also beliefs according to which the week has seven days because God created the world in 6 days and in the seventh he rested.

Moreover, even though various other civilizations had a week consisting of a different number of days, such as the Romans had 8 and the Egyptians 10 days in a week, over time they all adopted the 7 days.

### Work week and School week

These two notions define the time intervals in which the respective activities take place. They have nothing to do with the weeks of the year in the sense that they do not represent a specific week and do not influence in any way the number of the 52 weeks of a year.

In general, when we refer to workweek, we are actually talking about 5 days and not seven. This is because in general, professional activities take place from Monday to Friday, and the weekend is free. Of course, it's not the same for everyone. There are cases in which the workweek can have 6 days and the professional activity can take place from Monday to Saturday.

In a similar way, school week is the amount of time a week spent at school. Sometimes, out of all seven days of the week, it is possible for the school activity to take place only for four or five days. Regardless of this, the week that those days are part of is called school week.

### How come you've also heard of week 53?

The ISO 8601 implements well-defined parameters to eliminate doubts regarding date-and-time-related data between cultures and time-zones.

According to this standard there are Long years composed of 53 weeks, and Short years, those that have 52 weeks.

Years with 53 weeks are rarer and it happens with

• A year that begins (1 January) or ends (31 December) on a Thursday
• A Leap year that begins (1 January) Wednesday or ends (31 December) on a Friday

All other years are considered short years and have 52 weeks.

Therefore, in accordance with the rules of this standard, the following situations may occur: if December 31 is a day of:

• Monday - then is included in the first week of the following year
• Tuesday - then is included in the first week of next year
• Wednesday - then is included in the first week of the following year
• Thursday - is part of week 53 of the year it ends
• Friday - in Common year is part of week 52, and in Leap years is part of Week 53 of the year it ends
• Saturday - is part of Week 52 of the year it ends
• Sunday - is part of Week 52 of the year it ends

Example:

31 December 2017 is on a Sunday, therefore is included in the Week 52 of 2018
31 December 2018 is on a Monday, therefore is included in the Week 1 of 2019
31 December 2019 is on a Tuesday, therefore is included in the Week 1 of 2020
31 December 2020 is on a Thursday, therefore is included in the Week 53 of 2020

Let's stick to the generally accepted idea that a year has 52 weeks and let's make the best we can of each one.

Moreover, let's think about the fact that we have 168 hours every week. Therefore, this means that during the 52 weeks of the year we have so much time at our disposal!

In the article “168 hours each week” you'll find interesting information on a simple and efficient way to juggle the time we have at our disposal so we can live the life we want.

Mariana Holostenco

Contributor at PlanArty