What is first pass yield and how is it different from final yield?

First pass yield is the fraction of units passing all checks on the first attempt with no rework; final yield counts anything that eventually passes, including reworked units. In the example, FPY is 1,090 / 1,200 = 90.8%, but final yield is (1,090 + 75) / 1,200 = 97.1%. The 6.3-point gap is pure rework cost that final yield hides, which is exactly why FPY is the better process-health metric.

How do I calculate first pass yield?

Divide units that passed clean on the first attempt by total units started, then multiply by 100. In the example, 1,090 units passed first time out of 1,200 started, so FPY = 1,090 / 1,200 = 0.908 = 90.8%. Do not add back the 75 reworked units even though they eventually passed, and do not subtract the 35 scrapped units from the denominator; total started stays 1,200.

What is a good first pass yield percentage?

Benchmarks depend on process complexity, but world-class single stations often target 95% or higher, and 99%+ for mature automated operations. Below 90% usually points to a specific, fixable defect mode. The example's 90.8% is acceptable but not strong; the 6.25% rework rate signals real waste. Focus on the trend and per-station FPY rather than a universal target, since a 20-step line will always show lower rolled yield than one station.

Why is my first pass yield lower than my final yield?

Because final yield credits reworked units and FPY does not. Every unit that fails, gets reworked, and then passes lowers FPY while final yield still counts it as good. In the example, 75 reworked units create the gap between 90.8% FPY and 97.1% final yield. A large gap means your line is leaning on rework to hit shipping targets, which hides an upstream defect and inflates labor cost.

How do I combine first pass yield across multiple process steps?

Multiply the FPY of each step to get rolled throughput yield (RTY). If four stations each run 90.8% FPY, RTY = 0.908^4 = 0.679, or about 68%. This shows why even good-looking station yields collapse over a long line: small losses compound. RTY reveals the true probability a unit passes the entire process untouched, which is often far lower than any single station's number suggests.

Do scrapped units count in the first pass yield denominator?

Yes. Total units started includes everything that entered the process, so the 35 scrapped units stay in the denominator of 1,200. They simply never appear in the numerator because they did not pass. Removing scrap from the denominator would artificially raise FPY. FPY = 1,090 / 1,200 = 90.8%; the 2.9% scrap rate and 6.25% rework rate together account for the remaining 9.2%.

Quality and Inspection

First Pass Yield Formula

First pass yield (FPY) measures how many units pass inspection the first time without any rework. Use it to track process quality, set improvement targets, and compare stations or shifts.

Formula

First Pass Yield = Units Passed First Time / Total Units Started

Variables

Units Passed First Time: Units that passed all quality checks on the first attempt with no rework or repair
Total Units Started: All units that entered the process in the measurement window

Understanding the First Pass Yield Formula

First pass yield measures the fraction of units that clear every quality check on the first attempt with zero rework, repair, or adjustment. Unlike final yield, which counts anything that eventually ships as good, FPY exposes the hidden factory of touch-up and rework that final yield conceals. It matters because every reworked unit consumes labor, delays throughput, and often masks a process defect. FPY is the honest measure of whether your process makes it right the first time.

The inputs are simple counts pulled from your inspection or MES records: units that passed clean, and total units started in the window. In the example, 1,090 of 1,200 units passed clean, giving 1,090 / 1,200 = 0.908, or 90.8%. The 75 reworked units and 35 scrapped units are deliberately excluded from the numerator. The classic mistake is crediting reworked units that later passed, which inflated FPY would hide. For multi-step lines, multiply each station's FPY to get rolled throughput yield.

Read FPY against the cost of rework, not just as a pass percentage. World-class assembly often targets 95% or higher per station, and anything under 90% usually signals a specific defect mode worth a Pareto analysis. In the example, the 6.25% rework rate plus 2.9% scrap is where the money leaks, even though 90.8% sounds acceptable. Track FPY by station and shift to isolate the source, then attack the largest defect category first rather than spreading effort thinly across every symptom.

Worked Example

1,200 units were produced. 1,090 passed first time. 75 were reworked and passed. 35 were scrapped.

FPY = 1,090 / 1,200 = 0.908 = 90.8%
Rework rate = 75 / 1,200 = 6.25%
Scrap rate = 35 / 1,200 = 2.9%

Result: 90.8% first pass yield

Common Mistake

Counting reworked units that eventually passed as first-pass successes. FPY only credits units that needed no intervention. Including reworked units inflates FPY and hides the true cost of rework.

Frequently Asked Questions

What is first pass yield and how is it different from final yield?: First pass yield is the fraction of units passing all checks on the first attempt with no rework; final yield counts anything that eventually passes, including reworked units. In the example, FPY is 1,090 / 1,200 = 90.8%, but final yield is (1,090 + 75) / 1,200 = 97.1%. The 6.3-point gap is pure rework cost that final yield hides, which is exactly why FPY is the better process-health metric.
How do I calculate first pass yield?: Divide units that passed clean on the first attempt by total units started, then multiply by 100. In the example, 1,090 units passed first time out of 1,200 started, so FPY = 1,090 / 1,200 = 0.908 = 90.8%. Do not add back the 75 reworked units even though they eventually passed, and do not subtract the 35 scrapped units from the denominator; total started stays 1,200.
What is a good first pass yield percentage?: Benchmarks depend on process complexity, but world-class single stations often target 95% or higher, and 99%+ for mature automated operations. Below 90% usually points to a specific, fixable defect mode. The example's 90.8% is acceptable but not strong; the 6.25% rework rate signals real waste. Focus on the trend and per-station FPY rather than a universal target, since a 20-step line will always show lower rolled yield than one station.
Why is my first pass yield lower than my final yield?: Because final yield credits reworked units and FPY does not. Every unit that fails, gets reworked, and then passes lowers FPY while final yield still counts it as good. In the example, 75 reworked units create the gap between 90.8% FPY and 97.1% final yield. A large gap means your line is leaning on rework to hit shipping targets, which hides an upstream defect and inflates labor cost.
How do I combine first pass yield across multiple process steps?: Multiply the FPY of each step to get rolled throughput yield (RTY). If four stations each run 90.8% FPY, RTY = 0.908^4 = 0.679, or about 68%. This shows why even good-looking station yields collapse over a long line: small losses compound. RTY reveals the true probability a unit passes the entire process untouched, which is often far lower than any single station's number suggests.
Do scrapped units count in the first pass yield denominator?: Yes. Total units started includes everything that entered the process, so the 35 scrapped units stay in the denominator of 1,200. They simply never appear in the numerator because they did not pass. Removing scrap from the denominator would artificially raise FPY. FPY = 1,090 / 1,200 = 90.8%; the 2.9% scrap rate and 6.25% rework rate together account for the remaining 9.2%.