How to Connect and Sync a Thunderbird Calendar with Nextcloud

This should have been easy, but as all things it ended up hard. First, when I tried a simple import of my Thunderbird .ics calendar into my new Nextcloud install, I got ‘could not parse data’ errors. Wouldn’t end. After much searching it seems like there might be something in the .ics data that doesn’t work with new Nextcloud, or, my calendar file was over 1.2MB which apparently is too big for many systems.

The second problem was just the usual forgetting of how Nextcloud calendar jives with Thunderbird.

I’ll deal with both quickly for you.

How to Deal with the Parse Problems when Importing a .ics File from Thunderbird into Nextcloud

There were a few ways apparently to have dealt with this problem, but what finally worked for me well and very fast was this:

1. Create a new calendar in gmail/google
2. Import your Thunderbird .ics calendar in there (for some reason it works…)
3. Export it from google afresh
4. Import it into Nextcloud

How to Deal with the Annoying Pop-up Window problem in Nextcloud

I’ll hopefully file a bug report on this one day but when I was importing the newly-exported .ics file into Nextcloud, finally this time it started to work BUT the main ‘calendar settings’ window popped up in front of the actual import status dialogue window so I couldn’t perform the task. After hundreds of click-attempts to retrieve the barely-visible import status dialogue window (which still required one more action item and click from me to continue), I couldn’t get to it. So, what I found worked instantly was to just refresh the page (f5 key on keyboard) when you were in this situation and try again and be ready to *very carefully* mouse-over your options. Hope this helps

Syncing Thunderbird Calendar to Nextcloud Calendar(s)

Now that you have your calendar(s) working on Nextcloud and you can see your appointments there, it’s time to sync with Thunderbird. For some reason this is always hard for me but it’s actually not hard once you’ve done it once and refreshed yourself on the steps. To save you (and me) the refreshing part, here are the steps inside Thunderbird – and have your Nextcloud username and password handy before you start:

1. Go to calendar view
2. Bottom left pane “New Calendar”
3. Select the “On the network” option
4. Enter your Nextcloud username into ‘username’ field – keep this window open and available as we will come back to it shortly
5. Log into your Nextcloud account
6. Go to calendar
7. On the left pane, on right side of calendar name that you wish to sync, click the ‘edit and share’ pencil
8. Click the ‘copy internal link’ button. This will now be in your clipboard for pasting
9. Go back to Thunderbird and paste this URL into your url field in Thunderbird window
10. Click ‘Find Calendars’ button
11. Enter password for Nextcloud user when prompted
12. Wait while calendars are discovered
13. Select your calendar (or calendars) you wish to sync with the check box
14. Make sure ‘CalDAV’ option is selected in option drop down
15. Click ‘subscribe’ button
16. Wait. If your calendar has a lot to sync like mine it may take a while.

There you go. All synced up with modern Nextcloud 32 and Thunderbird in 2025.