The formula
FPY = units passing first time ÷ units entering the process
A step that receives 1,000 units, scraps 20 and reworks 80 before they pass has a final yield of 98% but a first pass yield of 90%: only 900 units passed without intervention.
Rolled throughput yield
For a line of several steps, multiply the first pass yields: four steps at 95%, 92%, 97% and 90% give a rolled throughput yield of 0.95 × 0.92 × 0.97 × 0.90 = 76%. Only about three in four units pass the whole line without rework, even though each step looks acceptable. RTY shows why small losses at each step matter.
Why FPY matters
- It reveals rework, which costs capacity, labour and lead time but is invisible in final yield.
- It points at the specific step and defect type to improve.
- It is a leading indicator for customer complaints and cost of quality.
Using FPY on a tier board
Track FPY per line or step per shift, with target and trend, and record the defect types behind the misses. A falling FPY is a problem for the Tier 1 huddle today; a step that is repeatedly the lowest is a problem for structured root cause work.
Common mistakes
- Counting reworked units as first-time good.
- Measuring only at final inspection, so the step that caused the rework is hidden.
- Setting FPY targets without recording the defect types that would let the team improve it.