How to Count Days and Weeks Correctly
Inclusive dates, elapsed time, and ISO weeks: understand which convention your calculation uses.
Read articleWhat Week Is It
Use what week is it with Calculator 360.
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How to use this calculator
Find the ISO 8601 week number of an explicitly chosen date. ISO weeks begin on Monday, and their year can differ from the calendar year around New Year.
Choose the relevant mode and units, enter the needed values, and review the result and its stated limits.
Calculated from the values you enter using the shared calculator engine.
Frequently asked questions
What does this tool calculate?
Find the ISO 8601 week number of an explicitly chosen date. ISO weeks begin on Monday, and their year can differ from the calendar year around New Year.
Which inputs are used?
The calculation uses the values and units you enter in this form.