Preventive maintenance cost: the price of prevention, made visible

Every few months the lubrication routes run, the filters get swapped, the belts get checked, all on schedule. The work orders close without drama: no breakdown, no call-out, nothing to show for the effort except equipment that simply kept running. Prevention is quiet by design, and quiet things are easy to stop valuing.

Preventive maintenance cost makes that quiet investment visible. It puts a percentage on what you spend keeping failures from happening, so you can weigh it honestly against what you spend cleaning up after them.

What it actually measures

PM cost is the share of your total maintenance spend that goes on fixed-interval tasks, work done on a time or run-hours schedule regardless of the equipment's measured condition on the day. It includes the labour, materials, services and contractor costs on PM work orders, along with operator-performed PM such as scheduled lubrication and cleaning.

How to work it out

Preventive maintenance cost = (PM cost ($) × 100) / Total maintenance cost ($)

In a month, PM work orders come to $227,563, contractor PM to $23,587 and operator PM to $7,300, against a total maintenance cost of $567,345.

Preventive maintenance cost = ($258,450 × 100) / $567,345 = 45.6%

Just under half the budget went on scheduled prevention. Set beside the corrective cost share each month, this is how you watch the balance tip, ideally, from reaction towards prevention.

More is not better

Here is the point that surprises people, and it is the most important thing this metric can teach you: spending more on PM does not automatically buy you more reliability, and past a point it buys you less. Every time you open a healthy machine to service it, you risk leaving it slightly worse than you found it, a misaligned coupling, a contaminated bearing, a gasket not quite seated. The evidence is sobering. When one paper industry inspected the bearings it had been replacing on a fixed schedule, only a twentieth were anywhere near failure; a third had nothing wrong at all, and most of the rest carried only minor damage the maintenance itself had caused. A large naval facility found that a tenth to a fifth of all its maintenance was rework, much of it defects introduced by time-based PM. And failures cluster tellingly in the first weeks after an intrusive job, the infant mortality that careful, non-invasive work avoids. The goal, then, is not the most PM but the right PM, done well, verified after the fact, and steadily handed over to condition monitoring wherever a machine can simply be watched instead of opened.

The root of it is a fact about failure that took the maintenance world a long time to accept: most failures are not driven by age. Only a minority of failure modes wear out on a predictable schedule; the majority arrive more or less at random, untouched by how recently the machine was serviced. So for much of what you maintain, a fixed-interval overhaul cannot prevent the failure it is aimed at, yet it still carries the full risk of disturbing a machine that was running perfectly well. Spending more on calendar-based PM, in other words, often means paying to introduce risk against failures it was never able to stop. The money is far better aimed at the wear-out tasks that genuinely respond to it, and at the condition monitoring that catches the rest.

What good looks like

There is no formal cost benchmark for PM, and it shadows PM hours closely, where the working guide is somewhere around 15 to 25 per cent of total maintenance effort, varying with the age and type of your assets. The cost figure also quietly polices efficiency: if your PM task counts hold steady while the cost share climbs, you have a spending problem rather than a workload one, and that is worth catching early.

Where it can mislead you

• Use the same time basis every period; mixing monthly and annual figures makes the trend lie.
• Your work-order system has to separate PM from other work cleanly, or the percentage means nothing.
• Minor fixes made during a PM, under the same work order, count as PM cost. Work that balloons well beyond the planned scope should be reclassified as corrective.
• PM cost depends heavily on how old and complex your assets are, so measure against your own history before reaching for an industry average, and never read a rising figure as automatically good; it may simply mean you are doing more intrusive work than the equipment needs.

PM cost is the twin of PM hours, the money beside the time. Read together, they keep your prevention programme honest: large enough to hold failures at bay, disciplined enough that it is not quietly buying risk, and humble enough to know that the best maintenance is often the machine you were wise enough not to open.