# 6.7. What is the week number?

## Description

This article is from the Calendars FAQ, by Claus Tondering claus@tondering.dk with numerous contributions by
others.

# 6.7. What is the week number?

International standard ISO-8601 (mentioned in section 6.6) assigns a

number to each week of the year. A week that lies partly in one year

and partly in another is assigned a number in the year in which most

of its days lie. This means that

Week 1 of any year is the week that contains 4 January,

or equivalently

Week 1 of any year is the week that contains the first

Thursday in January.

Most years have 52 weeks, but years that start on a Thursday and leap

years that start on a Wednesday have 53 weeks.

Note: This week numbering system is not commonly used in the United

States.

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