The international ISO 8601 definition of a week is mainly used in European and Asian countries for numbering weeks.
Current week number today - September 26, 2023 is
Monday, September 25, 2023 – Sunday, October 1, 2023
This definition of a week is used in the USA, Canada and most Latin American countries, Australia, Japan, Israel, South Korea and others to number weeks.
Current week number today - September 26, 2023
Sunday, September 24, 2023 – Saturday, September 30, 2023
The week number
The week number is often used to coordinate appointments or deadlines. The calendar year is sequentially divided into numbered calendar weeks. The year begins at the beginning of January with the first calendar week, continues through the current calendar week and ends at the end of December with Week Number 52 or 53.
However, on what weekday does a week begin? When exactly does the first calendar week begin and what is the number of the current week? How does it look at the end of the year? We will clarify these and other questions for you below.
On what weekday does the week begin?
The calendar week, standardised by the International Organisation for Standardisation (ISO), begins on Monday as deduced from the work week and school week, and ends with Sunday. This standardised calendar week is used mainly in Europe and Asia. On the other hand, the calendar weeks in North and South America, Australia and Japan start on Sunday and end on Saturday. In the Arab world, Saturday is the beginning of the week.
When does the first week of the year begin?
This question is quite easy to answer for the calculation of the calendar weeks in North and South America, as well as in Australia and Japan. For example, the first calendar week always begins on the first of January and ends on the following Saturday.
However, it is somewhat more difficult to answer when the first calendar week begins in Europe and Asia: In the internationally standardised calendar week system used in Europe and Asia, the first Thursday of the year must be in the first calendar week. This means that the first calendar week must contain at least four days of the new year and thus a maximum of three days of the first calendar week can be in the old year.
If 1st of January is Wednesday, then the first calendar week begins on Monday, 30th December. This 1st calendar week then contains two days of the old year (Monday and Tuesday) and five days of the new year (Wednesday to Sunday).
On the other hand, if 1st January is Friday, then the first calendar week does not begin until Monday, 4th January. The previous week would have contained only three days of the new year (Friday, Saturday, and Sunday).
Unlike in America, for example, the first week of the calendar does not necessarily begin on 1st January, but usually a few days earlier in the previous year. This ensures that each calendar week (i.e., from the first of the current calendar week to the last calendar week) always consists of seven days.
How is the current week number determined?
The current Week Number is obtained by counting the number of weeks from the first Monday of the first calendar week to the Monday of the current week. In the American method of calculation, the weeks are counted on the basis of Sunday. The Week Number today is then identified by the consecutive number and can also be defined by the date of the beginning and end of the week.
Are Week Numbers internationally regulated?
Yes, Week Numbers are internationally standardized by ISO 8601. The ISO (International Organization for Standardization) then provides an international recommendation for the calendar week system, which is generally used, especially in Europe and Asia. Nevertheless, the other type of calculation presented here has prevailed, especially in North and South America, as well as in Australia and Japan.
Are there other methods for determining the current Week Number?
Yes, as we have already seen, the American method of calculation differs from the standardised ISO method in Europe and Asia.
Although the numbering of the current calendar week is always based on the definition of the first calendar week, this can be done differently:
According to the ISO standard, the week always begins on Mondays. In North America and Latin American countries, Australia, Japan, Israel and South Korea, it begins on Sundays. In the Arab world, the week begins on Saturday.
While the first week of the ISO standard in many other countries is partly in the old and new year, the first day of the week starts exactly on January 1st. This is more intuitive than with the ISO standard, but then, the first and last week of the year usually consists of less than seven days.
This can lead to misunderstandings in the case of international appointments, which is why a more precise specification of the current Week Number based on the current date is advisable in such cases.
Determine current Week Number with the Week Number Calculator
With the Week Number Calculator, you can calculate the respective week not only for the actual week but also for any other date. You can also determine the respective calendar week using a date.
More online calculators
As source for the information in the 'Week Numbers' category, we have used in particular:
Last update on September 25, 2023
The page of the 'Week Numbers' category was last changed by Michael Mühl on September 25, 2023. In addition, the page is continuously reviewed editorially and corresponds to the current status.
Changes in this category "Week Numbers"
- Publication of the Week Number Calculator
- Editorial revision of this page