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Use the Week Number Calculator to find the week number for a specific date, or to find which 7 dates are included in a numbered week.

The results from the Week Number Calculator vary according to your country settings because different countries use different rules for calculating week numbers. Change country settings: My Units – Site Customization

FAQ: How Does the Week Number Calculator Work?

Is Sunday or Monday the first day of the week?

According to International Standard ISO 8601, Monday is the first day of the week. However, several countries, including the United States, Canada, and Australia, do not follow this standard and usually use Sunday as the first day of the week on their calendars.

To change which day is counted as the first of the week, click Expand for More Options and make your selection in the drop-down menu below First day of week:

Is the US week not a standard week?

According to International Standard ISO 8601, Monday is the first day of the week. However, several countries, including the United States, Canada, and Australia, do not follow this standard and use Sunday as the first day of the week on their calendars.

What is ISO 8610?

The International Standard ISO 8601 is the most common week numbering system in the world, where Monday is the first day of the week followed by Tuesday, Wednesday, Thursday, Friday, Saturday, and with Sunday as the seventh and final day. Using ISO 8601 can help diminish uncertainty and confusion when communicating internationally.

How do I set the calculator to ISO 8601?

To force the results to be presented in the ISO 8601 format, click Expand for More Options, and choose the following settings:

  1. Week Year Start Month:
    January
  2. Week Year Start Date:
    1
  3. When does week 1 start:
    Week 1 has at least 4 days on/after start date
  4. First day of week:
    Monday

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