A four-session training plan needs four actual calendar entries at the intended interval. A repeat setting that merely says weekly can create twice as many meetings as expected, while an unlimited series can continue after the work ends.

Write the intended dates before opening the event editor. For example, four Monday sessions two weeks apart, starting on 5 October 2026, fall on 5 October, 19 October, 2 November and 16 November. The written list becomes the check against the generated calendar.

Configure the pattern and its stopping rule

Rehearse in an existing private local calendar without attendees. Create an event through File, New, Event, check the selected calendar, and enter its first date and duration. Give the rehearsal an obvious test title so it cannot be mistaken for an approved booking.

In Repeat, choose Custom. Set a Weekly pattern, an interval of every two weeks and the intended weekday. For this example choose the option to create four appointments. Thunderbird also offers an end-date limit and an unlimited choice; these express different stopping rules.

Use a count when the requirement is a fixed number of sessions. Use an ending date when the requirement is a calendar boundary, then verify how many occurrences that rule produces. Do not assume the two choices always yield the same schedule.

Inspect occurrences rather than only the repeat dialog

After saving, visit each of the four expected dates. Check the title, starting time and duration. Also inspect the intervening Mondays: those weeks should not contain this test session.

Look at the next potential recurrence, 30 November. It should be absent. This final boundary check catches an unlimited series that looks correct during the first month.

If the dates differ, inspect the original starting date, selected weekday, interval and stopping rule separately. Correct the rehearsal and compare the entire list again instead of fixing individual visible occurrences until the pattern becomes hard to understand.

Use the verified pattern when preparing the real schedule, with its calendar ownership and participant arrangements reviewed separately. The private rehearsal establishes recurrence arithmetic; it does not send invitations or confirm anybody's availability. Remove the clearly identified rehearsal after recording the accepted date list.

Sources: Thunderbird documentation.