Week Number Calculator

Calendar Week Calculator - Calendar Weeks for All Years

Week Numbers ﹣ Calculator

With the Calendar Week Calculator, you can use a date to calculate the corresponding calendar week. Conversely, you can use the calendar week to determine the date of the beginning and end of the week you are looking for. You can use the international ISO 8601 calculation method for Europe and Asia and the American calculation method for calendar weeks as the internationally relevant method for calculating calendar weeks.

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Important links and information about the calendar week calculator

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Annual Calendar Week Overview

The following table lists the number of calendar weeks and calendar days for each year. It is also indicated if it is a leap year. The links in the second column take you to the overview pages of calendar weeks for the whole year.

Annual overview
Year CW Number of ISO calendar weeks Days Leap year
2021 Calendar weeks 2021 52 365
2022 Calendar weeks 2022 52 365
2023 Calendar weeks 2023 52 365
2024 Calendar weeks 2024 52 366
2025 Calendar weeks 2025 52 365
2026 Calendar weeks 2026 53 365
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List of All Calendar Weeks

Are you looking for specific calendar weeks? Get the detailed descriptions of all calendar weeks here.

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More Information on the Current Calendar Week

On the special page Current Calendar Week, you will always find the currently valid calendar week. In the navigation, you can select each individual calendar week or, for example, all historical calendar weeks 2022 or select the very latest calendar weeks 2023.

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Tips for Making Entries in the Week Number Calculator

Depending on the selection made in the input of the calculator, different input fields open, which we describe in the following.

Calculation of

Please select the value that you want to calculate. After selecting "Week number", the week number is calculated for the entered date. After selecting the "start and end of a week number" the start and end date for the entered week number are calculated.

Date input

Day

Please enter the day, i.e., the day of the month for calculating the week number.

Month

Please enter the month for the week number calculation.

Year

Please enter the year for the week number.

Week number entries / calender week

Week number

Please enter the week number for the calculation of week start and week end.

Year

Please enter the year of the week number for the calculation of week start and week end.

Calculation method

Select the method of week number calculation. Available are "International according to ISO", "North American calculation" and the "Arabic calculation", which are described in detail below.

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Calculation methods supported by the Week Number Calculator

International calculation according to ISO

The international ISO 8601 definition of a week is used mainly in European and Asian countries for numbering weeks:

Weeks start on a Monday, and the first week of the year includes January 4. This means that up to three days from the previous year may be included in the first week of the current year, and up to three days from the current year may be included in the last week of the previous year.

In other words:

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

Two examples of the first week number according to ISO 8601

  • If January 1 falls on a Wednesday, the first calendar week begins on Monday, December 30. This first week then contains two days of the old year (Monday and Tuesday) and five days of the new year (Wednesday to Sunday).
  • However, if January1 falls on a Friday, the first calendar week begins on Monday, January 4. This is because the previous week would have contained only three days of the new year (Friday, Saturday and Sunday).

North American calculation of week numbers

In the USA, Canada and most Latin American countries, as well as Australia, Japan, Israel, South Korea and other countries, a different system is used for numbering the weeks.

In contrast to the ISO standard, Sunday is the first day of the week, which then ends with Saturday. In addition, the first calendar week – regardless of the day of the week – always begins on 1 January.

In other words:

  • The first week of a year always starts on January 1 and ends on the following Saturday.
  • The last week of a year always begins on the last Sunday of the year and ends on December 31.

Examples

  • If January 1 falls on a Wednesday, the first week of the year begins on that Wednesday and consists of four days (Wednesday, Thursday, Friday and Saturday).
  • If December 31 falls on a Tuesday, the last week of the year begins on Sunday, December 29 and consists of three days (Sunday, Monday and Tuesday).

The rule that the first week always begins on January 1 is more intuitive than in the ISO standard, since the last calendar week always ends with the final week of the year, and the first week always begins with the new year. However, at the turn of the year, there are usually partial weeks of less than seven days, while the ISO calendar weeks always consist of whole weeks.

Arabic calculation of week numbers

In Arab countries, the system of week numbering is similar to the North American method of calculation just described. Unlike the latter, however, the week does not begin with Sunday, but with Saturday. Thus, the week ends on Friday. Apart from that, the first calendar week always starts on January 1 here as well, regardless of the day of the week.

In other words:

  • The first calendar week of a year always starts on January 1 and ends on the following Friday.
  • The last calendar week of a year always begins on the last Saturday of the year and ends on December 31.

Examples

  • If January 1 falls on a Wednesday, the first calendar week starts with that Wednesday and consists of three days (Wednesday, Thursday and Friday).
  • If December 31 falls on a Tuesday, the last calendar week begins on Saturday, December 28, and consists of four days (Saturday, Sunday, Monday and Tuesday).

Also, in the Arabic method of calculation, the rule that the first week always begins with January 1 is more intuitive than in the ISO standard, where the last week always ends in the current year and the first week begins with the new year. Likewise, at the turn of the year, there are usually partial weeks of less than seven days, while the ISO calendar weeks continue to consist of whole weeks.

Other definitions

There are many other definitions for numbering weeks.

In some companies, the first week begins in the middle of the year in order to accurately reflect their fiscal year, which differs from the calendar year.

In the U.S., the week predominantly begins on Sunday, but sometimes the beginning of the first week of the year is defined as in the ISO 8601 definition, i.e., not January 1.

Since the numbering of calendar weeks is not very common in the U.S., the counting method used in the calculator was chosen to reflect the way people speak in casual conversation:

"Week one is the first week of the year, and it starts on January 1. The weeks are then numbered consecutively, with each successive week starting on Sunday.

Source information

As source for the information in the 'Week Numbers' category, we have used in particular:

Last update on December 3, 2022

The pages of the 'Week Numbers' category were last editorially reviewed by Michael Mühl on December 3, 2022. They all correspond to the current status.

Previous changes on June 25, 2021