Date & Time calculator

Week Number Calculator

Find the week number for a selected date.

FormulaWeek is calculated from the nearest Thursday in the ISO week year

Formula

ISO week estimate

Week is calculated from the nearest Thursday in the ISO week year

Early January dates can belong to the last ISO week of the previous year.

FAQ5 common questions for this calculator.

FAQs

Which week numbering does this use?+

It uses ISO-style week numbering where weeks start on Monday.

How does the Week Number Calculator calculate the result?+

For the Week Number Calculator, it uses the ISO week estimate: Week is calculated from the nearest Thursday in the ISO week year. Early January dates can belong to the last ISO week of the previous year.

What information do I need to use the Week Number Calculator?+

For the Week Number Calculator, enter the relevant dates, times, timezone, or calendar settings requested by the form. Exact dates matter because month lengths, leap years, and boundary days can change the result.

How accurate is the Week Number Calculator?+

Week Number Calculator is accurate for the values and assumptions entered on this page. It uses the ISO week estimate. Recheck the inputs before relying on the estimate.

What should I check before using the Week Number Calculator result?+

For the Week Number Calculator, check the date and time fields, date format, timezone, daylight-saving changes, inclusive or exclusive endpoints, and whether weekends or holidays should count.

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Date & Time guide

How to use the Week Number Calculator

Find the week number for a selected date. The page also explains the ISO week estimate and shows a practical example: Early January dates can belong to the last ISO week of the previous year.

  1. 1

    Enter your details

    Enter the values for the week number calculator scenario you want to check.

  2. 2

    Check the calculation

    Review the result alongside the ISO week estimate: Week is calculated from the nearest Thursday in the ISO week year.

  3. 3

    Compare scenarios

    Change one or more inputs to see how they affect the week Number Calculator result before you use the estimate.