keymodels
First pass yield (FPY)
When and how should first pass yield (fpy) be applied?
Contents
Helps managers answer: How efficient are our internal operational processes?
First pass yield measures the proportion of units that complete a process step correctly on the first attempt, without repair, rework, retesting or scrap. It reveals quality losses that final output counts can hide.
When to use it
- Answer the key performance question: “How efficient are our internal operational processes?”
- Assess this KPI within the Operational processes and supply chain perspective.
- Plan data collection, formula use, reporting frequency, and data-source requirements for this KPI.
- Compare results against the targets, benchmarks, examples, or trend guidance available for this KPI.
Origins
FPY grew from the quality-control principle of producing conforming output correctly the first time. Its lineage runs through statistical process control, total quality management, lean production and Six Sigma rather than one inventor. The measure counters final yield, which may count a repaired item as successful and thereby conceal extra labour, delay, material and capacity consumed by the initial failure.
What it is
Perspective: Operational processes and supply chain perspective.
Key performance question: How efficient are our internal operational processes?
At a single step, FPY compares units that pass the first time with all units entering that step. A failure remains a first-pass failure even if an employee immediately fixes it and the unit ultimately ships.
For a sequence of steps, multiplying step yields produces rolled throughput yield: the estimated probability that a unit passes the entire flow without first-pass failure. Averaging step percentages is generally inappropriate because it does not represent that cumulative probability.
The measure requires explicit conformance criteria and process boundaries. It can be applied to physical products, transactions or service cases, provided entry, success and rework are observable on a common basis.
How to use it
Measurement
Map the process into meaningful steps. For each, define a unit, the specification for first-pass success, the point of entry and every activity that counts as rework, repair or retest.
Data collection method
Count entering and first-pass-conforming units with sensors, workflow events or controlled manual records. Reconcile scrap, routing changes and units still in process. Use representative sampling only when complete monitoring is impractical, and report the sampling uncertainty.
Formula
FPY for a step = (units completing the step without defect or rework / units entering the step) × 100
Rolled process yield = FPY step a × FPY step b × FPY step c × … × FPY step n
Use proportions in the multiplication and convert the final result to a percentage.
Frequency
Automated FPY can be monitored continuously with alerts for meaningful shifts. Manual sampling should follow a documented cadence that captures changes in product, shift, supplier and equipment condition.
Source of the data
Use production, workflow, inspection and rework records taken directly from the operational process.
Cost/effort in collecting the data
Automation requires initial configuration, calibration and maintenance. Manual counting can be more expensive over time and is vulnerable to inconsistent classification. The cost should be justified by the value of finding hidden rework and process instability.
Target setting/benchmarks
An FPY of 100% is the ideal, but the practical target should reflect process capability, risk, product mix and the cost of failure. Historical guidance has described a Sigma rating of 5 as equivalent to 12 months of production at 100% yield without defect or rework; do not assume that simplification is a universal statistical equivalence. Use observed capability and customer requirements to set the target.
Example
Consider a four-step assembly flow for unit A. Inspection after each step records first-pass failures:
100 units enter step 1; 95 pass.
95 units enter step 2; 92 pass.
92 units enter step 3; 88 pass.
88 units enter step 4; 88 pass.
The rolled calculation is:
FPY process = FPY step 1 × FPY step 2 × FPY step 3 × FPY step 4
FPY process = 95% × 96.8% × 95.6% × 100% = 87.9%
The example shows how moderate losses at individual steps accumulate across the full route.
Top practical tip
Make invisible rework visible. Define first-pass success with frontline employees, record every fix even when completed immediately, and show step-level losses beside the rolled result. A non-punitive reporting culture is essential because helpful employees often repair defects without logging them.
Top pitfall
Do not optimise the metric by weakening inspection, rerouting failures outside the boundary or pressuring people to hide rework. FPY measures conformance at the defined check, not customer value or process capability by itself. Pair it with defect severity, scrap, cost of poor quality, throughput and downstream outcomes.