Week Number Calculator
Find the ISO week number, day of year, days remaining, quarter and more for any date.
How to Use the Week Number Calculator
Select any date to see its ISO week number, day of year, days remaining in the year, day of week, quarter and whether it falls in a leap year.
Understanding ISO Week Numbers
- ISO 8601 — weeks start on Monday and the first week contains the year's first Thursday
- Week 1 — the week containing January 4th
- Range — week numbers run from 1 to 52 (or 53 in some years)
- Business use — widely used in project planning, payroll and scheduling
Frequently Asked Questions
What is an ISO week number?
ISO 8601 defines week 1 as the week containing the first Thursday of the year. Weeks start on Monday. This is the international standard used in business and project planning.
Can a year have 53 weeks?
Yes. Years that start on a Thursday (or start on a Wednesday in leap years) have 53 ISO weeks.
What is "Day of Year"?
Day of year counts how many days have passed since January 1st. For example, February 1st is day 32.
How is the quarter calculated?
Q1 is January-March, Q2 is April-June, Q3 is July-September, Q4 is October-December.
More Date & Time
Date Difference Calculator
Calculate the exact difference between two dates in years, months, days, weeks, hours and minutes.
Open tool →Timezone Converter
Convert times between timezones instantly. Supports 28+ world timezones with DST handling.
Open tool →Countdown Timer
Set a target date and time, then watch a live countdown showing days, hours, minutes and seconds.
Open tool →Stopwatch
Precise online stopwatch with start, stop, reset and lap time recording. Centisecond accuracy.
Open tool →Pomodoro Timer
25-minute work and 5-minute break cycles with progress bar, session counter and phase tracking.
Open tool →Date Formatter
Format any date in 12 patterns including ISO 8601, US, EU, RFC 2822, Unix timestamp and relative.
Open tool →