Why does my recurring class show up on the wrong weekday?

Usually a time zone problem or a mismatch between the first occurrence date and the BYDAY value. Both must agree.

Can I change one occurrence without breaking the series?

Yes, with an exception date or by editing that single instance in the calendar app. The underlying rule still applies to the rest.

Recurring class schedules: getting weekly and biweekly rules right

A weekly class is one rule, not fifteen events. How to encode weekly, twice-weekly, and alternating-week timetables so your calendar stays clean and editable.

One rule beats many events

A lecture that meets every Tuesday for 14 weeks can be stored as a single event with a repeat rule, or as 14 separate events. The first form is easier to edit — move the room once and the whole term updates.

The second form is what you get when a tool expands the series during export. It still works, but any change means touching 14 events.

The three patterns worth knowing

Weekly: FREQ=WEEKLY;BYDAY=TU;UNTIL=20261215T235959Z. Use it for a class that meets once a week.

Twice weekly: one event per weekday, each with its own weekly rule. Emitting a single event with BYDAY=TU,TH is valid, but separate events are easier to edit when the two sessions have different rooms.

Alternating weeks: FREQ=WEEKLY;INTERVAL=2;BYDAY=TU. This is the one people get wrong, because the class appears every other week, not every week.

Always set an end date

A repeat rule with no end date runs forever. Your calendar will show classes during the holidays and after the course finishes.

Use the last teaching day of term as the end boundary, which is usually one week before the exam period.

Exceptions and cancellations

When a single session is cancelled, the clean way is an exception date rather than deleting the event — the rule stays intact and only that instance disappears.

If your tool exports a series plus a cancellation, check both events in the file. A missing exception is a meeting you will show up for and nobody else will.

Verify before the term starts

Open the imported series and count the instances. A 14-week course should produce 14 occurrences, or 7 if it alternates.

Then check one instance mid-term against the syllabus. If week 8 lands on the wrong date, the start date or the interval is off.

FAQ

Why does my recurring class show up on the wrong weekday?: Usually a time zone problem or a mismatch between the first occurrence date and the BYDAY value. Both must agree.
Can I change one occurrence without breaking the series?: Yes, with an exception date or by editing that single instance in the calendar app. The underlying rule still applies to the rest.

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