Date & Time calculator
Week Number Calculator
Find the week number for a selected date.
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.
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?+
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?+
Find the week number for a selected date.
How accurate is the Week Number Calculator?+
Week Number Calculator applies the formula and assumptions shown on this page. Results may be rounded for readability, so verify changing rates, thresholds, medical guidance, or legal rules with the cited source or a qualified professional.
What should I check before using the Week Number Calculator result?+
Check that the units, dates, rates, and assumptions match your situation. Change one input at a time to understand which values have the largest effect on the result.
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
Enter your details
Enter the values for the week number calculator scenario you want to check.
- 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
Compare scenarios
Change one or more inputs to see how they affect the week Number Calculator result before you use the estimate.
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