Week Number Calculator
Find the ISO week number, day of year and days remaining for any date.
Results
What week number is it? Many businesses use ISO week numbers for invoicing, sprint planning, production schedules and reporting. Enter any date to get its ISO week number (1-53), day of year, days remaining and percentage of the year elapsed. ISO weeks start on Monday - the first week of the year contains January 4.
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Frequently asked questions
The ISO 8601 standard numbers weeks 1-53. Week 1 is the week containing the first Thursday of the year (or equivalently, the week containing January 4). Weeks always start on Monday.
Week numbers simplify scheduling across countries and calendar systems. 'Ship by W12' is clearer than 'mid-March' when teams span time zones. Manufacturing, logistics and project management rely heavily on week numbering.
Yes. Years that start on Thursday (or leap years starting on Wednesday) have 53 ISO weeks. This happens roughly every 5-6 years. Examples: 2020, 2026, 2032.
Day of year (1-366) is used in agriculture (planting schedules), meteorology (weather records), ordnance surveys and Julian date calculations. January 1 = day 1, December 31 = day 365 or 366.
ISO weeks start on Monday and week 1 contains January 4. US convention starts weeks on Sunday and week 1 contains January 1. The total week count between dates is the same.