PM frequencies are comforting. Thirty days. Ninety days. Quarterly. Annual. Nice round numbers you can put on a calendar and pretend you’ve tamed chaos.
They look responsible. They feel controlled. They make dashboards happy.
They are also usually wrong.
If you’re building a PM program from scratch, frequency is one of the first decisions people rush to lock in. And that rush is how maintenance teams quietly build failure into the schedule.
Because frequency doesn’t come from calendars. It comes from reality. And reality doesn’t care what day it is.
Where PM Frequencies Actually Come From
Most PM frequencies are inherited, not designed.
They come from:
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An OEM manual written in a clean lab
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A spreadsheet copied from another plant
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A legacy CMMS that nobody wants to touch
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A “that’s how we’ve always done it” conversation from 2009
None of these sources know how your equipment is actually used.
They don’t know your duty cycle.
They don’t know your environment.
They don’t know what operators do when nobody’s watching.
They don’t know what failed last month.
So we take a generic number and apply it universally. Same interval. Different reality.
That’s how PM frequencies start lying.
Calendar-Based PMs Assume the World Is Stable
They assume wear is predictable.
They assume loads are consistent.
They assume operating conditions don’t change.
None of that is true.
Machines don’t fail on schedules. They fail when stress, heat, vibration, contamination, and fatigue cross a threshold. Sometimes that takes six months. Sometimes it takes six days.
A bearing doesn’t care that it’s only been 27 days since the last PM. If lubrication is wrong or load is higher than expected, it’s already planning its exit.
This is why PM tasks must evolve as living documents instead of stone tablets, because fixed frequencies only make sense if nothing else changes. And everything changes.
Over-Frequent PMs Create Their Own Failures
Too much PM is not harmless.
Every time you open a machine, you introduce risk:
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Fasteners loosen
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Seals get disturbed
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Dirt gets inside
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Components get handled unnecessarily
Over-maintenance is how perfectly good parts get damaged by good intentions.
When frequencies are too aggressive, technicians rush. Steps get skipped. Tasks become muscle memory instead of inspections. PMs turn into motion without meaning.
You don’t prevent failures. You just touch the equipment more often.
Under-Frequent PMs Are Easier to Spot (After the Fact)
Under-maintenance looks obvious. Failures between PMs. Alarms. Downtime. Meetings where someone asks why nobody caught this.
But here’s the uncomfortable truth.
Most teams don’t respond by questioning the task itself. They respond by debating strategy. PM vs predictive maintenance vs run-to-failure. Sensors. Vibration analysis. Oil sampling.
All useful tools. All distractions if the basic task and frequency logic is wrong.
Technology doesn’t fix bad assumptions. It just documents them faster.
The Frequency Should Follow the Failure Mode
PM frequency should answer one question:
How fast does this failure develop in our environment?
Not in theory. Not in a manual. Not at another plant.
In this plant.
Some failures develop slowly and predictably. Some escalate overnight. Some only show up under specific conditions.
This is why the anatomy of a good PM task matters so much. If the task isn’t tied to a real failure mode, the frequency will always be a guess.
Good frequency comes from:
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Failure history
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Inspection results
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Missed defects
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Technician feedback
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Changes in operation
When those inputs change, the frequency should change too.
Failure Between PMs Is Feedback, Not Embarrassment
A failure between PMs isn’t proof that PMs don’t work. It’s proof that the interval is wrong, the task is incomplete, or both.
The worst response is defending the schedule.
The right response is asking:
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Did we inspect the right thing?
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Did we inspect it often enough?
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Did we miss early indicators?
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Did conditions change?
Every failure is data. Ignoring it because the calendar says you were “compliant” is how PM programs drift into fiction.
Why Frequencies Stay Wrong for So Long
Because changing them feels risky.
Changing frequency means:
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Admitting the old one was wrong
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Touching the CMMS
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Explaining decisions to leadership
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Breaking habits technicians rely on
So teams leave bad frequencies in place and quietly accept the consequences.
PM compliance stays green. Equipment keeps failing. Everyone pretends these things aren’t related.
They are.
Start With a Baseline, Then Let Reality Rewrite It
You don’t need perfect frequencies on day one. You need reasonable ones.
Start with intervals that make sense for the failure mode. Run them. Observe. Adjust.
That’s how frequencies become accurate. Not by guessing harder. By listening longer.
A PM program that never revisits its intervals isn’t disciplined. It’s stubborn.
Build PM Frequencies That Reflect Reality
If you want PM task lists that start with sensible baseline frequencies and are designed to be adjusted as conditions change, the PM Task List Library gives you a practical foundation.
The tasks are built around real failure modes and realistic inspection logic, so frequency becomes something you refine over time instead of something you blindly defend.
Calendars don’t prevent failures.
Understanding does.