Week Number Calculator

Find the ISO week number for any date, along with a full-year week calendar.

Select Date

Select a date to see its week number

Documentation

How It Works

This calculator uses the ISO 8601 standard. Weeks start on Monday, and Week 1 is the week containing the year's first Thursday. The ISO week year may differ from the calendar year at the start/end of the year.

The year calendar shows all weeks for the ISO year of the selected date. Click any week row to jump to that week's Monday.

ISO 8601 Rule

  • • Weeks start on Monday
  • • Week 1 has the year's first Thursday
  • • 52 or 53 weeks per year
  • • Jan 1–3 may be in week 52/53 of prior year

Disclaimer: For informational purposes only.

Frequently Asked Questions
How to Use

About the Week Number Calculator

What it calculates

This week number calculator handles date arithmetic, time zones, calendars, and scheduling utilities. Find the ISO week number for any date, with week boundaries and days remaining.

When to use it

Use for planning events, deadlines, workdays, and time-zone aware calculations.

Example

Adjust the inputs above to model your specific scenario with the Week Number Calculator.

Explore More

Related Calculators

Date +/-

Add or subtract years, months, and days from a date.

Leap Year Calculator

Check if any year is a leap year and find upcoming leap years.

Time Zone Converter

Convert time across multiple time zones instantly.

Workday Calculator

Calculate working days between dates, excluding weekends and holidays.

Calendar

Interactive monthly calendar with week numbers, day info, and quick navigation.

Date Duration

Calculate the duration between two dates in years, months, and days.