Week Number Calculator

Find the ISO week number for today or any date, and see which dates a week covers.

How to use week number calculator

  1. Choose a date
  2. Read its ISO week number and ISO year
  3. Check that week’s Monday-to-Sunday date range

Worked example

January 1, 2021

ISO week 53 of 2020

How the result is calculated

ISO weeks begin Monday. Week 1 contains January 4 and the year’s first Thursday, so late December can belong to the next ISO year.

Inputs stay in your browser. You can use this tool without joining the waitlist or creating an account.

From a calculation to a daily glance

Keep your next week in view.

Use Weekly Calendar to see the same week’s dates and your enabled calendar events. Do not assume every widget style prints ISO week numbers.

  1. 1Add the events you want to see to your calendar.
  2. 2Enable that calendar in the app.
  3. 3Add Weekly Calendar; use Edit Widget → Design to choose its look.
Get early accessExplore widget designs

Web results do not automatically sync to the app. Setup is manual; calendar events appear through your enabled calendars.

February
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CelebrationWorkshopMeetingProject reviewTeam dinner
Weekly Calendar · example design from the app

Frequently asked questions

What week number is it right now?
The calculator shows the current ISO 8601 week number for today by default, along with the date range that week covers. Pick any other date to see its week number instead.
How are ISO week numbers defined?
Under ISO 8601, weeks start on Monday and week 1 is the week that contains the year's first Thursday. This is the standard used across most of Europe and in business and project planning, so a year can have 52 or 53 weeks.
Can I see week numbers on my iPhone calendar?
Yes. The Monthly Calendar Widgets week and month widgets give you a clean weekly view on your Home Screen, so you always know where you are in the month without opening the calendar app.

More free calendar tools