Loading calculator...
Loading calculator...
Find the ISO week number for any date and the start/end dates of that week.
ISO 8601 Week Number:
Week 1 is the week containing the first Thursday of the year.
This is the international standard. The ISO week starts on Monday and ends on Sunday. Some years have 53 weeks.
ISO 8601 week numbers are a standard way to number weeks in a year. Week 1 is the week containing the first Thursday of the year, and weeks always start on Monday.
Yes. Days in early January or late December can belong to a different ISO year. For example, January 1, 2021 was in ISO week 53 of 2020.
Most years have 52 ISO weeks. A year has 53 weeks if January 1 falls on Thursday, or if it's a leap year and January 1 falls on Wednesday or Thursday.
The US week number system (used in some spreadsheets) starts weeks on Sunday and may define week 1 differently. ISO weeks always start on Monday.
Yes. Many businesses use ISO week numbers for financial reporting, production scheduling, and payroll periods. It provides a consistent reference across years.