Why the number matters
Maintenance budgets are argued in money, and downtime is usually argued in feelings. “That pump keeps failing” does not get a spare pump approved. “That pump cost us 140,000 last year in lost output and emergency repairs” usually does. The point of this calculator is to put a defensible number on something everyone already knows is expensive.
What to count, and what not to
Lost margin, not lost revenue. If a line producing 40 units an hour stops, you lose the margin on those units: revenue minus the material, energy and variable costs you also did not spend. Using revenue overstates the cost and makes the number easy to dismiss. And if lost output can be made up later on spare capacity, the real loss is the cost of making it up, typically overtime, not the margin.
Idle labour is real even if wages are fixed. People paid to wait are paid for nothing. Count the fully loaded hourly cost, including social charges, for the people who cannot do productive work while the equipment is down.
Per-event costs are often the surprise. Express shipping for a part, a contractor call-out at night, the batch that has to be scrapped, the hours it takes to bring a process back to steady state. These do not scale with downtime hours, so a plant with many short stops can lose more than one with a few long ones.
Leave out what you cannot defend. Lost customer goodwill and reputation are real, but if you cannot put a number on them that a finance manager would accept, mention them in words instead. A conservative number that holds up beats a big one that gets thrown out.
A worked example
A process line loses 1,200 in margin for every hour it stands still. Six operators wait at 25 an hour. Each breakdown needs about 2,500 in emergency repairs and 800 in scrap and restart losses, and lasts eight hours on average. Six breakdowns a year.
One hour of downtime costs 1,350. One breakdown costs about 14,100 once the per-event costs are added. Over a year that is close to 85,000. Making the stops a quarter shorter is worth about 16,000 a year in hourly costs alone, and preventing a quarter of the breakdowns outright would save around 21,000. That is the budget a reliability improvement has to fit within to pay back in a year.
From cost to action
Once you know what an hour of downtime costs, two decisions get much easier. The first is spare parts: the critical spare parts calculator takes the hourly cost and tells you which parts are worth keeping on the shelf. The second is planned work: most long outages are lost to preparation, not repair, and the shutdown readiness checklist is built around that.
And if you are not yet recording breakdowns consistently, start there. The equipment log template gives you a failure log with exactly the columns this calculator needs: downtime hours and cost per event.
Frequently asked questions
What is a typical cost of downtime per hour?
It varies enormously, from a few hundred for a small workshop to many thousands for continuous process plants. Industry surveys often quote large averages, but they mix very different industries. Your own number, built from your own margin and labour costs, is the only one worth using in a budget discussion.
Should I include the cost of planned maintenance?
No. This calculator is about unplanned downtime. Planned stops are scheduled, prepared and usually cheaper per hour because people, parts and production plans are ready. The difference between the two is exactly what good maintenance planning buys you.
How do I estimate lost margin per hour?
Take the output per hour at normal production, multiply by the contribution margin per unit (selling price minus variable costs), and adjust for whether the output can be recovered later. For utilities, use the penalties, the cost of backup supply or the value of the service lost instead.
Is any of my data stored?
No. All calculations run in your browser and nothing you enter is sent anywhere.
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