Find week number.
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Current week
This is the current week according to the ISO 8601 standard.
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Enter a date (dd-mm-yyyy) or week number (1-53).
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About week numbers
ISO 8601: The International Standard
Week numbers in Denmark and most of the world follow the international ISO 8601 standard. This standard ensures that week numbers are consistent across borders and systems.
The system is designed to avoid ambiguity in data exchange. When you refer to "week 29", everyone following ISO 8601 will understand exactly which period is meant.
Key principles in ISO 8601
- A week starts on Monday. This is one of the most fundamental principles.
- Week 1 is the first week of the year that contains a Thursday. This also means that week 1 always contains January 4th.
- A year has either 52 or 53 weeks. If January 1st is a Thursday, or if it's a leap year and January 1st is a Wednesday, the year has 53 weeks.
- The first few days of a year may belong to the last week of the previous year, and the last few days of a year may belong to week 1 of the next year.
Example: Transition from 2024 to 2025
Tuesday, December 31st, 2024 is part of week 1, 2025. This is because the Thursday of that week (January 2nd, 2025) falls in 2025, which defines the entire week as the first week of the new year.