Week Number Calculator
See the current week number at a glance, look up the week number for any date, and browse a full-year calendar with ISO 8601 week numbers.
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2026
About Week Numbers
Week numbers (also called ISO week dates) follow the ISO 8601 standard, where weeks start on Monday and the first week of the year contains the first Thursday of that year. This standard is widely used in business, manufacturing, and project management across Europe and many other regions.
The TimeGlobe Week Number Calculator shows you the current ISO week number at a glance, along with the day of the year and how many days remain. Use the date picker to find the week number for any date, or browse the full-year calendar view to see all 52 or 53 weeks laid out by month.
Frequently Asked Questions
What is ISO 8601 and why does it matter for week numbers?
ISO 8601 is an international standard for representing dates and times. Under this standard, weeks start on Monday, and the first week of the year is the one containing the first Thursday. This avoids ambiguity and is the standard used in most business and government contexts worldwide.
Can a year have 53 weeks?
Yes. Most years have 52 weeks, but some have 53. A year has 53 ISO weeks if January 1 falls on a Thursday, or if it's a leap year and January 1 falls on a Wednesday. This happens roughly every 5 to 6 years.
Why does the first week of the year sometimes start in December?
Under ISO 8601, Week 1 is the week containing the first Thursday of January. This means that the last few days of December may belong to Week 1 of the following year, and the first few days of January may still belong to the last week of the previous year.
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