๐
Date & Time
Week Number Calculator
ISO week numbering, used across Europe and in most business software, defines week one as the week containing the first Thursday of the year. That means early January can belong to the last week of the previous year.
How it works
Date
ISO week number
ISO week year
Day of the year
ISO weeks in the year
Quarter
Frequently asked questions
How do I use the Week Number Calculator?
Fill in the fields above โ the result recalculates instantly as you type. Everything runs in your browser, so the values you enter are never collected or stored.
Is this calculator free?
Yes. It is completely free, requires no account, and works on phones, tablets and desktops.