This problem is over a year old and no one has come up with an answer? See https://support.mozilla.org/en-US/questions/1419857.

I'm testing in Beta 131.0b3

In Calendar

• click on 'New Event'

I set up the following as a test.

• Calendar = Home
• Title = TEST ME DATE
• Category = Status
• Start 25/09/2024 at 6pm
• End 25/09/2024 at 7pm

• Repeat: Click on drop down to see options and select 'Custom'
• At top - Repeat choose 'Weekly'
• Every 1 week
• On: Wed
• Select 'Repeat until' option and select 22/01/2025

It shows example of what I've selected in calendar style - click on 'Next Month' to see more. Click on 'OK'

Click on 'Save and Close'

Result: Every wednesday from 25/09/2024 and including 22/01/2025 has an event called TEST ME DATE.

I tested the same process on my 115.15.0 version and had no issues. Image below shows Event I created and I've also included the last date it displays on.

I also tested this method:

• click on 'New Event'

I set up the following as a test.

• Calendar = Home
• Title = TEST ME ALT
• Category = None
• Start 25/09/2024 at 7pm
• End 25/09/2024 at 8pm

• Repeat: Click on drop down to see options and select 'Weekly'
• Until: select 22/01/2025
• Click on 'Save and Close'

Images shows the two I set up.

I'm not seeing this issue no matter which method I use.

Thanks for testing. I tried again and get this result: (Thunderbird 115.14.0 (64-bit) on Fedora 39 on Dell XPS 13)

Click New event Click "All Day Event" Title "Test Calendar" Start 9/14/24 End 9/14/24 Select Repeat: Custom Select "Monthly" under Repeat. Select "The Second Saturday" Range of occurrence: Repeat until 1/11/25 Click "ok" Click ctrl-L Nothing at 1 /11/25

Select "edit all occurrences" for "Test Calendar" and I see this:

   Repeat: Custom  Occurs the second Saturday of every month effective 9/14/24 until 1/10/25.

Thunderbird has changed the end date that I entered when I created the event. (The same experience that Brodie.Bernardi found a year ago.)

(I wondered if I should put 1/11/25 as the "End" on the main new even page. That event-command creates multiple events every day for as far into the future as I checked.)

P.S. If I don't use "All day event," but put in 00:01 until 23:59, the problem doesn't occur.

Thanks for your reponse, data and information. AS you say this seems specific to 'All Day Event'. I repeated using specifically your test data and agree with your results.

Then I used the same data but set 'REpeat until: 18/01/2025 (UK date) - basically chose the 3rd sat. Result - it set to the date I desired - Sat 11th Jan 2025

I edited the event and set Repeat until : 12/01/2025 Result - it set to the date I desired - Sat 11th Jan 2025

The 'REpeat until' seems to mean up until but not inclusive.

Whilst this is a workaround in this instance, it's probably not expected. If people enter a specific dat to be the last date then if it complies with the second saturday rule, iy would be expected to be included.

I'll see there is some bug reported on this.

Thanks, Toad-Hall, for your efforts.

Someone has recently created a bug report on this. I've added the link below just in case anyone wants to follow progress. https://bugzilla.mozilla.org/show_bug.cgi?id=1917314