← Blogby Marcell Almeida

How to find the ISO week number for any date

Pick a date — get ISO week number, week boundaries, and YYYY-Www label.

Sprint planning and payroll often use ISO week numbers, not calendar months. The ISO Week Number Calculator returns week 1–53 with start and end dates.

Try it — select any date

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How it works

  1. Select date — any calendar day.
  2. Week number — ISO 8601 week of year.
  3. Week range — Monday-start week boundaries.

ISO vs US weeks

ISO weeks start on Monday. Week 1 is the week with the year's first Thursday. US "week of year" conventions may differ.

Date tools

Pair with Age Calculator or Timezone Converter for scheduling.

The How to find the ISO week number for any date is free, runs locally, and never sends your data to a server. More converter tools at maratool.com.