PM schedule software does one job and can do it in two very different ways, and the difference decides whether a schedule stays honest. Either the next occurrence of a job is calculated from when the last one was actually completed, or it is fixed to a calendar laid down at setup. The first keeps the interval real through the inevitable slippage; the second drifts from the first missed job onward and produces a calendar nobody trusts by the second quarter. This page is about that choice and the two behaviours that go with it.
Ask what happens to the next three dates when a job is late
This question separates the two kinds of product in one answer. Floating from completion means a job done two weeks late pushes the next one out by two weeks and the interval is preserved. Fixed calendar means the next date arrives two weeks after the late completion, the job gets deferred, and the drift compounds.
Insist on the load in hours, not jobs
Sixty jobs a month is a fact and 66 technician hours is a plan; only the second can be compared against the people you have. On the worked example this site publishes that is $3,168 a month at a $48 loaded rate. Products that show a calendar and no hours let schedules be agreed that were never staffable.
Deferral has to be visible without running a report
The list of jobs rescheduled more than once is the earliest warning a maintenance function gets. Behind a report it is worth nothing, because nobody runs reports until something has already gone wrong.
Two clocks, because most sites have two
Calendar intervals for what degrades with time and weather, running-hours intervals for what degrades with work. A product that holds only one will have the other tracked in a spreadsheet beside it, and two schedules of record is worse than one spreadsheet.
Questions people ask about pm schedule software
Should PM dates float or stay fixed?
Float, for almost everything. Fixed dates make sense only where an external body sets them, such as a statutory inspection.
How far ahead should the schedule be visible?
A quarter is usually right: far enough to order parts and book cover, near enough that the dates still mean something.
What if a job is done early?
It should pull the next one forward, for the same reason lateness pushes it back. The interval is the thing being controlled, not the date.