First Pass Yield, or FPY, measures the proportion of units that complete a process correctly the first time without rework, repair, retest, or repetition.

It answers a useful question:

How often does the process get the work right on the first attempt?

That makes FPY a strong indicator of hidden quality loss.

Basic formula

For a single process step:

FPY = Good units completed without rework ÷ Total units entering the process

If 1,000 units enter a process and 920 pass correctly without rework:

FPY = 920 ÷ 1,000 = 92%

The remaining 8% represents work that required correction, failed, or was otherwise not right the first time.

Why FPY matters

Final inspection can hide instability.

Suppose a process produces 1,000 units and ships 990 good units.

That may look like a 99% yield.

But what if 150 units required rework before shipping?

The final output may appear strong while the process is consuming labor, equipment time, materials, and capacity to correct defects.

FPY exposes that hidden factory.

This connects directly to Cost of Poor Quality, because rework and retest create internal failure cost even when the customer never sees the defect.

FPY vs final yield

Final yield asks how many units eventually become acceptable.

FPY asks how many were acceptable without additional correction.

Both can be useful, but they answer different questions.

A process can have:

  • high final yield;
  • low first-pass yield.

That combination usually indicates significant hidden rework.

Rolled Throughput Yield

When a product passes through several process steps, FPY can be calculated at each step.

The combined probability of passing every step correctly the first time is often called Rolled Throughput Yield.

For example:

  • Step 1 FPY = 95%
  • Step 2 FPY = 98%
  • Step 3 FPY = 97%

Even though each individual step looks relatively strong, the end-to-end first-pass performance is lower because the losses accumulate.

This is why end-to-end thinking matters.

Define the denominator carefully

FPY is only useful when the measurement is operationally defined.

Clarify:

  • what counts as a unit;
  • when the unit enters the process;
  • what counts as acceptable;
  • what counts as rework;
  • how scrap is treated;
  • whether retest counts as failure;
  • whether repeated service contacts count as rework.

Without a clear definition, different teams can report different FPY values for the same process.

Use FPY to find process weakness

FPY is most useful when it triggers investigation.

If FPY falls, ask:

  • Which defect categories increased?
  • Which product families are affected?
  • Which machines or shifts show the pattern?
  • Where does rework occur?
  • What changed in material, method, machine, measurement, or people?

4M Analysis and Root Cause Analysis can help structure the investigation.

FPY and process capability

FPY is an outcome measure.

Process Capability describes how process variation relates to specification limits when the process is stable.

A process can have poor FPY because of:

  • excessive variation;
  • centering problems;
  • setup errors;
  • intermittent special causes;
  • measurement problems;
  • workmanship errors;
  • unstable equipment.

Do not assume the metric alone identifies the cause.

Common mistakes

Counting reworked units as first-pass good

This defeats the purpose of the metric.

Measuring only final inspection

The rework may have occurred earlier.

Comparing FPY across unlike processes

Different complexity and defect opportunities can make comparisons misleading.

Improving the metric without reducing the problem

Changing inspection rules is not process improvement.

Ignoring measurement-system quality

If inspection is inconsistent, FPY becomes unreliable. Measurement System Analysis may be needed.

A practical FPY routine

  1. Define the process step.
  2. Define first-pass acceptance.
  3. Capture total inputs.
  4. Capture units requiring rework, repair, retest, or scrap.
  5. Calculate FPY.
  6. Stratify the losses.
  7. Prioritize dominant defects.
  8. Investigate causes.
  9. Implement countermeasures.
  10. Monitor whether FPY improves and stays improved.

The practical lesson

FPY prevents rework from hiding process weakness.

A process that eventually produces acceptable output may still be expensive, unstable, and capacity-constrained.

First Pass Yield shows how much of the work is actually right the first time.

Additional connections

This topic also connects with Work Sampling. That relationship is useful when the team needs to extend the method into a wider improvement system.