What's the current Week Number?

Week 39 start date is Monday, 25 September 2023 and end date is Sunday, 01 October 2023 as per ISO-8601 standard.

The ISO week-numbering year starts at the first day (Monday) of week 01 and ends at the Sunday before the new ISO year (hence without overlap or gap). It consists of 52 or 53 full weeks. The first ISO week of a year may have up to three days that are actually in the calendar year that is ending; if three, they are Monday, Tuesday and Wednesday. Similarly, the last ISO week of a year may have up to three days that are actually in the calendar year that is starting; if three, they are Friday, Saturday, and Sunday. The Thursday of each ISO week is always in the calendar year denoted by the ISO week-numbering year.

There are several mutually equivalent and compatible descriptions of week 01:

• the week with the year's first Thursday in it (the formal ISO definition),
• the week with 4 January in it,
• the first week with the majority (four or more) of its days in the starting year, and
• the week starting with the Monday in the period 29 December – 4 January.

As a consequence, if 1 January is on a Monday, Tuesday, Wednesday or Thursday, it is in week 01. If 1 January is on a Friday, Saturday or Sunday, it is in week 52 or 53 of the previous year (there is no week 00). 28 December is always in the last week of its year.

The week number can be described by counting the Thursdays: week 12 contains the 12th Thursday of the year.

Current year weeks with start and end date :