Aftermarket, Field Service & Service Parts worked example

Service Parts Demand at 99% stocking readiness: a worked example

This scenario runs the service parts demand calculation on the strong side: 99% stocking readiness, with every other input held at its documented default. a spare parts planner needs to translate installed-base failures or maintenance events into a stocking requirement

The inputs for this scenario

  • Parts used per service event: 1.8 parts/event (unchanged)
  • Forecast service events: 420 events (unchanged)
  • Stocking readiness: 99 % (raised for this scenario; the documented default is 95)
  • Usable demand yield: 92 % (unchanged)

Working through the calculation

  • Applying the documented formula (Gross service parts demand = parts used per service event × forecast service events) to the inputs above produces each figure below.
  • At this operating point the engine returns 689 service parts for usable service parts demand, the number this scenario is built around.
  • At this operating point the engine returns 756 service parts for gross service parts demand.
  • At this operating point the engine returns 7.56 service parts for demand missed by stocking readiness.
  • At this operating point the engine returns 59.88 service parts for demand lost to forecast yield.

How this compares with the baseline

  • Against the tool's baseline example, where stocking readiness sits at 95% and the headline result is 661 service parts, this scenario comes in 4.21% above the baseline at 689 service parts.
  • Use it to set replenishment quantities and safety stock for a service parts SKU over a forecast period. Treat this as a target state: the delta against the baseline quantifies what the improvement is worth before you commit to chasing it.

Results at a glance

  • Usable service parts demand: 689 service parts (headline result)
  • Gross service parts demand: 756 service parts
  • Demand missed by stocking readiness: 7.56 service parts
  • Demand lost to forecast yield: 59.88 service parts

Run it with your numbers

  • Every input above is editable in the live Service Parts Demand calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.