Week Number — Free Online Tool
Find the ISO week number, day of year, days remaining, and quarter for any date.
About Week Number Calculator
The Week Number Calculator tells you the ISO 8601 week number for any date, along with its ISO year, the day of the year, how many days remain until year end, and which calendar quarter it falls in. It is handy for payroll, project planning, fiscal reporting, and anyone who works with week-based schedules.
All values are computed instantly in your browser using the international ISO standard, where weeks start on Monday and week 1 is the week containing the year's first Thursday. Select a date or jump to today, and the full breakdown appears at once.
How to Use Week Number Calculator
- Select the date you want to analyze.
- Click Calculate to see its ISO week number and related details.
- Use the Today button to jump straight to the current date.
- Read the ISO week, day of year, days remaining, and quarter from the result cards.
Key Features
Calculates the ISO 8601 week number for any date
Shows the matching ISO year, which can differ near year boundaries
Displays the day of the year and days remaining
Identifies the calendar quarter (Q1 to Q4)
Instant client-side results with one-click jump to today
Works on desktop, tablet, and mobile browsers
Frequently Asked Questions
What is an ISO week number?
ISO 8601 weeks start on Monday, and week 1 is the week that contains the year's first Thursday. This standard is widely used in business, finance, and project planning across Europe and beyond.
Why can the ISO year differ from the calendar year?
Days in late December can belong to week 1 of the next ISO year, and early January days can belong to the last week of the previous ISO year. The tool shows the ISO year so the week number always makes sense.
How is the day of the year calculated?
It counts the number of days from January 1 up to and including your selected date, so January 1 is day 1 and December 31 is day 365 or 366 in a leap year.
Which quarter does my date fall in?
The tool maps the month to a calendar quarter: January to March is Q1, April to June is Q2, July to September is Q3, and October to December is Q4.