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W26
ISO Week Number
Mon Jun 22 – Sun Jun 28, 2026
| Week # | Mon (Start) | Sun (End) | Months Covered | Quarter | Days |
|---|
Frequently Asked Questions
What week number is it today?
Today is in Week -- of 2026. ISO weeks start on Monday and end on Sunday.
How are ISO week numbers calculated?
ISO 8601 defines a week as starting on Monday. Week 1 of a year is the week that contains the first Thursday of the year (or equivalently, the week containing January 4th). This means January 1 can sometimes be in the last week of the previous year (Week 52 or 53).
How many weeks are in 2026?
2026 has 52 ISO weeks. The year starts on Thursday, January 1, and ends on Thursday, December 31. Week 1 of 2026 begins on Monday, December 29, 2025.
What is the difference between ISO week and calendar week?
ISO weeks (ISO 8601) always start on Monday. In the US, calendar weeks often start on Sunday. This means an ISO week number may differ from a US-style week number by 1 depending on the day. OnlineCalendar.org uses ISO 8601 week numbering.
When does Week 1 of 2027 start?
ISO Week 1 of 2027 starts on Monday, January 4, 2027 — because January 1, 2027 falls on a Friday, and Week 53 of 2026 covers Dec 28, 2026 – Jan 3, 2027.