Week Number Calculator

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Find the ISO 8601 week number for any date, plus the week of the year, day of the year, days left in the year and the calendar quarter. Free and instant.

Pick any date to see its week number and where it falls in the year.

ISO 8601 week –
Week of year –
Day of year –
Days left in year –
Quarter –
ISO 8601 weeks start on Monday; week 1 is the week containing the year's first Thursday, so early-January or late-December dates may belong to a neighbouring year's week. The simple week of year counts calendar weeks from 1 January.

About Week Number Calculator

The week number calculator answers “what week number is it?” for today or any date you pick. It reports the ISO 8601 week number — the standard used in business planning, logistics and much of Europe — alongside the simple week of the year counted from January 1.

Under ISO 8601, weeks start on Monday and week 1 is the week containing the year’s first Thursday. That is why a date in early January can belong to week 52 or 53 of the previous year, and late December can already sit in week 1 of the next — the calculator handles those edge cases for you.

To place the date in context, you also get the day of the year, the days remaining in the year and the calendar quarter. It is a quick, free reference for planners, project managers and anyone whose deadlines are expressed in week numbers.

How to use Week Number Calculator

  1. Pick a date, or click “Use today” for the current date.
  2. Read the ISO 8601 week number and the simple week of the year.
  3. Check the day of year, days left in the year and the quarter for extra context.

Frequently asked questions

Click “Use today” and the calculator instantly shows the current ISO 8601 week number, along with the day of the year, the days remaining and the current quarter.

The simple week of year counts calendar weeks from January 1, while ISO weeks start on Monday and anchor week 1 to the first Thursday. Around the new year the two systems can disagree by a week.

Yes. Under ISO 8601, years that start on a Thursday — or leap years starting on a Wednesday — contain 53 numbered weeks instead of the usual 52.

ISO week 1 must contain the year’s first Thursday. If January 1 falls on a Friday, Saturday or Sunday, it belongs to the closing week of the previous ISO year.

It numbers the date from 1 to 365 (or 366 in leap years), which is useful for ordinal date formats, progress tracking and quickly seeing how far into the year a date falls.
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