Weeknumber.io

Digital calendar

Add week numbers to your calendar

Import a transparent, all-day ISO week marker for each Monday in Google Calendar, Outlook or Apple Calendar.

Download ISO weeks (.ics)

Turn on built-in week numbers

Most calendar apps can show week numbers without importing anything. Menu names vary slightly between versions.

Google Calendar (web)

  1. Open Google Calendar on a computer and select the gear icon, then Settings.
  2. Under General, open View options.
  3. Tick Show week numbers. Google Calendar numbers weeks by ISO 8601 when the week starts on Monday; set Start week on to Monday in the same section.

Google Calendar (Android)

  1. Open the app menu and select Settings, then General.
  2. Turn on Show week number, and set Start of the week to Monday.

Outlook (classic desktop)

  1. Select File → Options → Calendar.
  2. Under Work time, set First day of week to Monday and First week of year to First 4-day week. This makes Outlook match ISO 8601.
  3. Under Display options, tick Show week numbers in the month view and in the Date Navigator.

New Outlook and Outlook on the web

  1. Open Settings → Calendar → View.
  2. Set the first day of the week to Monday and the first week of the year to First 4-day week.
  3. Turn on Show week numbers and save.

Apple Calendar (Mac)

  1. Open Calendar and choose Calendar → Settings (Preferences on older macOS).
  2. In General, set Start week on to Monday.
  3. In Advanced, tick Show week numbers.

iPhone and iPad

  1. Open the Settings app, then Calendar (on iOS 18 and later: Apps → Calendar).
  2. Turn on Week Numbers, and set Start Week On to Monday.

If the number shown is one higher than on Weeknumber.io for part of the year, the app is counting the week containing January 1 as week 1. Switch the first week of the year to "First 4-day week", or import the ISO markers below.

Import ISO week markers (.ics)

The file covers 2026-2028. Each marker is an all-day event on Monday and is marked transparent/free, so it should not reserve your availability. Import it into a separate calendar so you can hide or remove all markers together.

Google Calendar

  1. On a computer, open Google Calendar and choose Settings.
  2. Open Import & export, then select the downloaded .ics file.
  3. Choose a separate destination calendar and select Import.

Google notes that imported events do not stay synchronized with the source file. Read Google's official import instructions.

Outlook

  1. In Outlook's calendar, choose Add calendar.
  2. Select Upload from file, then choose the .ics file.
  3. Select the calendar where the week markers should appear and import.

Menu names can vary between Outlook on the web, new Outlook and classic Outlook. Use a separate calendar when possible. Read Microsoft's official import instructions.

Apple Calendar

  1. On Mac, choose File, then Import.
  2. Select the downloaded .ics file.
  3. Choose a separate calendar for the imported markers.

For a published calendar URL, Apple Calendar also supports File → New Calendar Subscription. Read Apple's subscription instructions.

Import versus subscription

This download is an importable snapshot, so it will not update automatically. A future subscription feed would stay current, but should be hosted at a stable public URL and tested across calendar clients before launch.