Micro Tools
Advertisement

Week Number Finder

Find the ISO week number for any date. See the week-year, the Monday-to-Sunday range of that week, and how many ISO weeks the year contains.

Pick a date

Result

Pick a date and press Get week number.

Advertisement

What an ISO week number is

ISO 8601 defines weeks as starting on Monday, with week 1 being the week that contains the first Thursday of the year. That means early January dates can belong to week 52 or 53 of the previous year, and late December dates can fall in week 1 of the next year. The tool also shows the exact Monday-to-Sunday range so there is no ambiguity.

Why week numbers matter

Project plans, manufacturing schedules, payroll cycles and European business culture all run on week numbers. Knowing that a deadline is "week 34" is more useful than a bare date when everyone plans in weekly blocks.

Related tools

Spin the wheelRandom picker wheel for names, decisions and giveaways. Countdown timerCountdown to any date, interval timer and stopwatch with laps. Random numbersRandom numbers, no-duplicate option.

Week Number Finder FAQs

Why does January 1 sometimes belong to week 52?
ISO week 1 is the week with the first Thursday. If January 1 falls on Friday, Saturday or Sunday, those days belong to the last week of the previous year.
Do ISO weeks start on Monday or Sunday?
Monday, always. The US convention of Sunday-start weeks is different and can give different week numbers.
How many weeks are in a year?
Usually 52, occasionally 53. The tool shows the count for the relevant week-year automatically.
What is the difference between week-year and calendar year?
The week-year is the year a week belongs to under ISO rules. Late-December days can sit in week 1 of the next week-year.
Can I use this for sprint planning?
Yes. Many agile teams label sprints by ISO week number, and the Monday-to-Sunday range shown here maps directly onto sprint boundaries.
Advertisement