Find the week number for a given date.
Select any date to instantly see its ISO week number and year for business calendar purposes....
Enter values to see the result.
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Choose the date you want to check using the date picker. This can be any date in the past, present, or future.
Instantly see the ISO 8601 week number for your selected date, following international business calendar standards.
Note the year the week belongs to (which may differ from the calendar year for dates in early January or late December).
Apply the week number to business reports, manufacturing schedules, project timelines, or any ISO week-based planning system.
ISO week numbers follow the ISO 8601 standard, where week 1 is the first week with at least 4 days in the new year. Weeks run Monday to Sunday, and each week belongs to the year that contains the majority of its days.
A year has 53 weeks when January 1st falls on a Thursday, or when it's a leap year and January 1st falls on a Wednesday. This happens because the ISO week system ensures complete 7-day weeks.
Week 1 is the first week of the year that contains at least 4 days of the new year. This means it's the week containing the first Thursday of January.
ISO weeks always start on Monday and end on Sunday. Some calendar systems (like in the US) start weeks on Sunday. This calculator uses the ISO 8601 standard, which is the international business standard.
ISO weeks start on Monday and week 1 contains the first Thursday. US week numbering often starts on Sunday and week 1 contains January 1st. ISO is the global business standard.
Yes! Many companies use ISO week numbers for fiscal reporting because it provides consistent week-based periods. However, verify that your company follows ISO 8601 rather than a custom fiscal calendar.
Following international business calendar standards.
Calculate a future date by adding a specific number of days.
Calculate a future date by adding a specific number of months.
Calculate a future date by adding a specific number of years.
Calculate a past date by subtracting a specific number of days.
Calculate a past date by subtracting a specific number of months.
Calculate a past date by subtracting a specific number of years.