We are currently in the 40th calendar week. It lasts from Monday, October 2, 2023 to Sunday, October 8, 2023.

The year 2023 is not a leap year and therefore has 365 days. The next leap year will be in 2024 with 366 days.

# The Calendar Week

The calendar week is also called CW. The first week of the year does not automatically begin with the first of January. It is right four times out of seven and wrong three times out of seven.

You can see why this is the case and, above all, which calendar week it is at the moment on .

## What is a calendar week?

The calendar week (CW) is a week that begins on Monday and ends on Sunday. The year usually has a total of 52 calendar weeks.

## When does the first calendar week of a year begin?

The first calendar week of a year is the week that contains at least four days of the new year.

For example, if January 1 falls on a Tuesday, the first week of the year begins Monday, December 31, because that week contains six days of the New Year (Tuesday, Wednesday, Thursday, Friday, Saturday and Sunday).

On the other hand, if January 1 falls on a Friday, the first calendar week of the new year begins on Monday, January 4, since the previous week only contained three days of the new year (Friday, Saturday, and Sunday).

### How did the ISO 8601 standard for calendar weeks come about?

In 1976 it was established that the week officially started on Monday. The first week of the year is the week that includes at least 4 of the first 7 days of January, i.e. the week in which January 4 falls. These two definitions were first defined in 1974 in the DIN 1355 standard. The same content is regulated by the ISO standard 8601 from 1988, which was adopted by the European Union in 1992 as EN 28601 and implemented in Germany in 1993 as DIN EN 28601.

### The year has 52 weeks, sometimes 53!

Thus, the majority of all years have 52 calendar weeks. Due to the annual extra day and the leap years, however, there is a year with 53 weeks every 5 to 6 years, such as the years 2004, 2009, 2015, 2020.Since there are no half weeks, some days belong to your calendar week on another year than the actual date (e.g. January 2, 2022 is still part of the 52nd week of the year 2021).