What is the What Week Is It??
Businesses, schools and factories often plan by week number: "delivery in week 46" or "exams in week 10". This page shows the current ISO 8601 week number, today's day of the year and the weeks left in the year.
You can also look up the week number of any date. For a full calendar with week numbers see the Year Calendar; for a progress bar of the year see Weeks Left in the Year.
How to use the What Week Is It?
- Open the page to see today's week number.
- Pick another date to find its week number.
- Read the day of the year and weeks left.
Formula
ISO week 1 is the week containing the first Thursday of the year; weeks start on Monday.
Example
Saturday 10 October 2026 is in ISO week 41 and is day 283 of the year.
How ISO week numbers work
Under ISO 8601, weeks run Monday to Sunday and week 1 is the week with the year's first Thursday. That means 1 January can belong to week 52 or 53 of the previous year, and some years have 53 weeks. The USA often uses a different system where week 1 starts on 1 January and weeks begin on Sunday.
Where week numbers are used
- Production and shipping schedules
- School and university timetables
- Payroll and timesheets
- Retail sales reports
More free date and time tools
Planning around dates usually needs more than one answer. These related tools work the same way, instantly in your browser and free:
- Days until any date: count down to an exam, trip or deadline.
- Date calculator: add or subtract days, weeks, months or business days.
- Date difference calculator: the exact time between two dates.
- Age calculator: your exact age in years, months and days.
- Time zone converter: the same moment in Pakistan, the Gulf, the UK and the USA.
- Online timer: a countdown with an alarm sound.
Frequently asked questions
What week number is it today?
The current ISO week number is shown at the top of this page.
Does the week start on Monday or Sunday?
ISO weeks start on Monday.
Can a year have 53 weeks?
Yes. Years starting on a Thursday (or a Wednesday in leap years) have 53 ISO weeks.
What day of the year is it?
The day number is shown below the week number.
How do I find the week number of a date?
Pick the date in the lookup box.
Is the What Week Is It? free to use?
Yes. The What Week Is It? on Custom Converter is completely free, with no sign-up, no daily limit and no watermark.
Does the What Week Is It? work on mobile phones?
Yes. It is built mobile-first and works on Android phones, iPhones, tablets and computers in any modern browser, with no app to install.