Maintenance & Reliability worked example

Preventive Maintenance Interval with historical hours between service-triggering failures of 1,600 hr: a worked example

This worked example runs the preventive maintenance interval numbers for a tougher week than the baseline: historical hours between service-triggering failures of 1,600 hr instead of the typical 3,200 hr. Estimate a protected PM interval in days from historical failure spacing, average daily run time, and a safety multiplier.

The inputs for this scenario

  • Historical hours between service-triggering failures: 1,600 hr (the input this scenario stresses; the baseline uses 3,200)
  • Average run hours per day: 20 hr / day (held at the documented default)
  • PM safety multiplier: 1.25 x (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Historical interval in days = historical hours between service-triggering failures รท average run hours per day.
  • Recommended PM Interval works out to 64 days at these inputs, and this is the headline figure for the scenario.
  • Historical Interval in Days works out to 80 days at these inputs.
  • Historical Hours Between Failures works out to 1,600 hr at these inputs.
  • Average Run Hours per Day works out to 20 hr / day at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where historical hours between service-triggering failures sits at 3,200 hr and the headline result is 128 days, this scenario comes in 50% below the baseline at 64 days.
  • Use it when setting or revising the frequency of a time-based PM in your CMMS, especially once you have enough failure history to know the real mean time between failures. A result at this level usually justifies acting on the stressed input before touching anything else, because every other figure in the table is downstream of it.

Results at a glance

  • Recommended PM Interval: 64 days (headline result)
  • Historical Interval in Days: 80 days
  • Historical Hours Between Failures: 1,600 hr
  • Average Run Hours per Day: 20 hr / day

Run it with your numbers

  • To rerun this with your own numbers, open the live Preventive Maintenance Interval calculator, set historical hours between service-triggering failures to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.