Find the ISO 8601 week number, ISO week date, US week number, day of year, quarter and leap year status of any date. Free online calculator. All processing runs locally in your browser. Your data is not uploaded to any server.
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How to Use
Find out which week a date belongs to, under the ISO 8601 rules as well as the simpler US convention, along with day of year and quarter.
Steps
Pick the date you are interested in.
Click Calculate.
Read the ISO week, the ISO week date and the US week number.
What the result shows
ISO 8601 week number and the ISO year-week reference.
The full ISO week date, for example 2026-W38-5-Friday.
The US week number, which counts from the first of January.
Day of year, days left, quarter, leap year status and Unix seconds.
Features
ISO weeks start on Monday and week 1 contains the first Thursday.
ISO year can differ from the calendar year at the turn of the year.
Day of year is exact, using 366 days in leap years.
All processing runs locally in your browser. Your data is not uploaded to any server.