Fixed and Variable Schedules
How a time-based work task decides when its next occurrence is due, and how occurrences are generated.
A time-based work task repeats on an interval — but there are two different answers to "when is the next one due?", and picking the wrong one is a common source of confusing schedules.
Fixed schedule
With a fixed schedule, occurrences land on the calendar regardless of when previous ones were completed. A quarterly filter change due January 1 puts the next occurrence on April 1 even if the January work slipped and was finished in February.
Use this when the calendar matters more than the interval: compliance inspections that must happen each quarter, seasonal work, anything where "we do this every January" is the actual requirement.
Variable schedule
With a variable schedule, the next occurrence is anchored to when the last one was completed. Finish the January service in February, and the next one lands three months from February, not from January.
Use this when the interval between services is what matters. A variable schedule never asks you to service something twice in two months just because the previous occurrence ran late — the gap between actual service dates stays honest.
A task can also be set not to repeat at all, for one-off planned work.
How occurrences appear
FMX doesn't pre-create years of future occurrences as records. Future occurrences are projected from the schedule, and an occurrence only becomes a persistent record once someone interacts with it — so a weekly task doesn't generate clutter, but the calendar still shows what's coming. Each occurrence that does come due gets its own status and history; see Work Task Occurrence Statuses.
A worked example
A facilities team sets up two tasks for the same rooftop unit. "Quarterly filter change" uses a fixed schedule — filters are cheap, and the team wants a predictable calendar rhythm, so even when the Q1 change happens late, Q2's occurrence stays on its original date. "Belt inspection and tension" uses a variable schedule every 6 months — when a slipped occurrence gets done 2 months late, the next one moves out 6 months from the completion date, because what matters is how long the belts have actually gone since the last inspection.