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Clear, practical guides on week numbers, the ISO 8601 standard, pregnancy weeks and the calendar tools we build.

2 articles

ISO 8601 3 min read

ISO 8601 Week Numbers Explained — Why January Can Be Week 53

ISO 8601 is the international standard for week numbering. Here's exactly how it works, why weeks start on Monday, and …

May 10, 2026 Read →

Week Numbers 3 min read

Most years have 52 weeks, but some have 53. Find out why, which years have 53 ISO weeks, and exactly how week numbers w…

May 1, 2026 Read →