Quality and Inspection

First-Pass Yield: What It Means and How to Improve It

First pass yield = units passing inspection without rework / total units started. Here is how to calculate FPY and rolled throughput yield across a multi-step process.

First pass yield equals units passing inspection without rework divided by total units started. If 950 out of 1000 parts pass first inspection, FPY = 95%. That sounds strong until you look across a multi-step process. In a 5 step process where each step runs 95% FPY, rolled throughput yield is 0.95^5 = 77.4%. That means only about 77 of every 100 parts make it through all five steps without touching rework.

Rolled throughput yield equals FPY at step 1 x FPY at step 2 and so on through the process. If step FPYs are 98%, 95%, 97%, 91%, and 99%, the 91% step is the biggest drag and the first place to work. Improving that single step from 91% to 96% raises RTY from 79.7% to 87.5% without changing anything else. FPY data should come from in-process inspection counts before rework, not from final shipment numbers after defects have been corrected. On many assembly and machining lines, best-in-class FPY is above 98%, while high-mix operations may struggle in the low to mid-90s.

The biggest FPY mistake is counting reworked parts as good parts. Final inspection may show 99% pass, but if operators reworked defects at prior steps, the true FPY is much lower. Another common error is measuring FPY only at final inspection, which hides where defects are actually created. Plants also mix startup loss, supplier defects, and process defects into one bucket, which makes root cause analysis slow. FPY must be tracked at each operation if you want the metric to lead action.

Use FPY to identify the most expensive quality problems first. Rework cost per unit equals rework labor time x labor rate plus rework machine time x machine rate plus added material. If rework takes 15 minutes at $35 per hour labor and 5 minutes on a $70 per hour machine, rework cost is $14.58 per defective unit. At a 5% defect rate on 10,000 units per month, that is $7,290 in monthly rework cost. The FPY result tells you where rework burden is hiding in the process.

Pair FPY with defect mode analysis to decide what to change. If one dimension creates 40% of failures, that tolerance or process variable deserves immediate attention. If failures cluster by shift, operator, or material lot, those are the first factors to investigate. Related metrics such as RTY, scrap cost, and Cpk help distinguish between a local workmanship issue and a broader process capability problem. FPY is not just a quality score, it is a map to the highest-cost defects in the route.

Published 2026-05-28.