Week Number Calculator
Find the week number of a date — or the dates of a given week number.
—ISO week number
—Week (Monday – Sunday)
—Week-numbering year
—Weeks in that year
—Day of the year
Dates of a week number
—Monday
—Sunday
● Everything is calculated in your browser. Nothing is sent anywhere.
How it works
ISO 8601 weeks start on Monday, and week 1 is the week containing the year's first Thursday (equivalently, 4 January). So 1–3 January can belong to the last week of the previous year, and some years have 53 weeks. This is the system used in Europe and in most business software. The US often counts weeks starting on Sunday instead.