Week Number Calculator

Shows the current calendar week number, calculates it for any day and calculates the date for any week number. The week number is defined in ISO 8601. This definition of the calendar week number is common in Europe. One week has seven days, begins with Monday and ends with Sunday. The first week is the one with the first Thursday of the year. Of this week, at least 4 days, which is the majority of days, are in this year. One year has 52 or 53 weeks. If the year begins with a Thursday, for leap years Wednesday or Thursday, it has 53 weeks, otherwise 52. The first week can contain days of the previous year, the last week days of the following year. Beginning and end of a year can also be in the week of the previous respectively following year.
In the upper part, the week number for one day can be calculated. In the lower part, the week number can be entered and the date of the week from Monday to Sunday will be shown.

Current week number:

123456789101112 / 12345678910111213141516171819202122232425262728293031 /
is in week number .


Week number 1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253
is from to .

Calendar week numbers are used particularly in the business world to provide concise and clear time specifications lasting one week. Often, this does not mean that the week is the entire period of time for an appointment, meaning that the appointment does not last the whole week, but rather that it only falls in the specified calendar week. An example of such an appointment is a repair works that have to be done at home or at the workplace. In the long term, this appointment is initially announced for a calendar week or a period of several calendar weeks and then usually specified a few days in advance with the day and time. This is due to the fact that many previous appointments have an unclear duration and subsequent appointments cannot be scheduled precisely any time in advance. Specifying a calendar week number allows for some flexibility.

Last updated on 12/20/2025. Author: Jürgen Kummer

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