Week Number
Current Week Number
45
Week 45 of 2026
ISO 8601 • week starts Monday
Week number for any date
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How ISO week numbers work
Under ISO 8601, weeks start on Monday and the first week of the year is the one containing the year's first Thursday — equivalently, the week containing January 4th. This is the standard used across Europe and in business, banking and manufacturing.
Because of this rule, the first days of January can belong to the last week (52 or 53) of the previous year, and late-December days can already fall in week 1 of the next year. A year has 53 weeks when it starts on a Thursday (or on a Wednesday in a leap year).
Frequently Asked Questions
- What week number is it right now?
- It is currently week 45 of 2026 under ISO 8601.
- When does the week start?
- In the ISO 8601 standard the week starts on Monday and ends on Sunday.
- How many weeks are in a year?
- Most years have 52 weeks; some have 53. A year has 53 ISO weeks when January 1st falls on a Thursday, or on a Wednesday in a leap year.
- Why is January 1st sometimes in week 52 or 53?
- Because a week belongs to the year that contains its Thursday. If early January days fall in a week whose Thursday is still in December, they keep the previous year's week number.