How to add it to your calendar
This is a subscription, not an import. Your calendar stays linked to the source, so corrections and new years arrive on their own. The "Add to your calendar" button offers shortcuts for the common apps. This section explains what happens behind them and how to do the same by hand.
Google Calendar
Click Google Calendar in the menu. calendar.google.com opens and asks "Add calendar?". Confirm, and the calendar appears next to your other calendars.
On a phone, do this in the browser, not in the app. The Google Calendar app cannot add a calendar from a link. Once you add it on the web, it shows up in the app too. If you cannot see it, open the settings of the app, find your account and switch the calendar on.
By hand: on the web, next to "Other calendars" click +, then "Subscribe to calendar" and enter the calendar address:
ad121182502d24eef2c249ca54e0638b11eb9400573848f17d2c1108d028806f@group.calendar.google.com
Apple Calendar (iPhone, iPad, Mac)
Click Apple Calendar. A subscription prompt opens. Confirm it. The step is the same on iPhone and Mac.
By hand on iPhone: Settings › Apps › Calendar › Accounts › Add Account › Other › Add Subscribed Calendar, then paste the address:
https://calendar.google.com/calendar/ical/ad121182502d24eef2c249ca54e0638b11eb9400573848f17d2c1108d028806f%40group.calendar.google.com/public/basic.ics
On a Mac: Calendar › File › New Calendar Subscription. Set auto-refresh to "every day".
Samsung Calendar (Galaxy phones)
Samsung Calendar cannot subscribe to a calendar address. It shows only the calendars of the accounts on your phone. So put this calendar in your Google account first, then switch it on in Samsung Calendar.
1. On the phone, open this page in the browser and click Google Calendar. Sign in with the same Google account the phone uses, then confirm "Add calendar?".
2. Open the Google Calendar app. Menu (the three lines, top left) › Settings › the name of the new calendar, under "Show more" if you do not see it. Turn Sync on.
3. Open Samsung Calendar. Menu (the three lines, top left) › Manage calendars › your Google account, then switch the calendar on.
If the calendar stays empty, open Settings › Accounts and backup › Manage accounts › your Google account › Sync account, and switch Calendar on.
Do not use "Import events" in Samsung Calendar. That copies the dates once, and they never update again.
Without a Google account, Samsung Calendar cannot do this at all. A separate app such as ICSx⁵ holds the subscription and shows it in Samsung Calendar.
Outlook
Outlook.com and Microsoft 365 on the web: click Outlook.com in the menu. By hand: Add calendar › Subscribe from web, then paste the address above.
Classic Outlook for Windows: File › Account Settings › Internet Calendars › New.
Everything else (Thunderbird, Fastmail, Proton, Nextcloud...)
Any app that offers "subscribe to a calendar by URL" or "network calendar" takes the same .ics address. Copy it with the Copy address button and paste it.
To look without a subscription: open in Google Calendar.