First Pass Yield, written FPY, is the share of units that go through a process step and come out right the first time, with no rework, no touch-up and no second attempt. It is calculated for one step at a time. FPY = Units Passing First Time Without Rework ÷ Units Entering the Step. A unit that fails, gets fixed and then passes does not count in the numerator.
The phrase "entering the step" matters. If 1,250 leads arrive at a crimping station, the denominator is 1,250 even if a few are set aside before crimping starts. Everything that came in is the base. The numerator is only what left the station good without anyone having to intervene.
In an automotive wire-harness plant the typical steps are cutting and crimping terminals onto wires, routing the wires on a form board, taping the bundle, and electrical continuity testing. Each gets its own FPY. The numbers are small on purpose: a station handling thousands of leads a day lives or dies on whether 94 percent or 98 percent of them pass first time.
Standard Procedure
- 1Define where the step begins and ends so everyone counts the same units.
- 2Count every unit that enters the step during the period.
- 3Count units that leave the step good without any rework, adjustment or retest.
- 4Divide the first-time-good count by the entering count.
Lesson Summary
- ✓FPY is calculated per step, using units entering as the base.
- ✓Any correction, however small, removes a unit from the first-time-good count.