What Is First Pass Yield?
Also known as: FPY, first time yield, right first time
Definition
First pass yield is the percentage of units that complete a process correctly the first time, without rework, repair, or retest. Units that eventually pass after rework are excluded, so the metric captures hidden factory loss.
First Pass Yield Explained
First pass yield is calculated as units passing on the first attempt divided by units entering the process. The distinguishing rule is that a unit which fails, gets reworked, and then passes counts as a failure. Traditional yield counts it as a success, which is why traditional yield can read 98 percent while the plant runs a full-time rework cell. The gap between final yield and first pass yield is precisely the size of the hidden factory.
For multi-step processes, rolled throughput yield multiplies the first pass yield of every step. This exposes a mathematical reality that surprises most teams: ten sequential operations each running a respectable 97 percent produce a rolled yield of 0.97 to the tenth power, or 73.7 percent. Only about three units in four pass through the entire routing untouched. Managing operations individually against a 95 or 97 percent target while ignoring the rolled number is why line-level yield performance persistently disappoints.
Accurate measurement requires that failures be recorded at the point of first detection, which is exactly the practice most floors resist. If an operator quietly reworks a part at the station, first pass yield is inflated and the loss becomes invisible. Serialized tracking in an MES with a pass or fail disposition at each test or inspection point is the reliable mechanism; relying on scrap tickets alone will always understate the problem because rework generates no scrap ticket.
First pass yield is directly connected to capacity. Every reworked unit consumes labor, machine time, material, and inspection a second time, and on a constrained resource that time is unrecoverable throughput. Plants often discover that raising first pass yield from 82 to 91 percent frees more effective capacity than the equipment purchase they were evaluating, at a small fraction of the cost.
Why It Matters
- Exposes the hidden factory of rework, retest, and repair that final yield metrics systematically conceal.
- Rolled throughput yield makes it clear why routings with many steps deliver poor overall performance despite good individual numbers.
- Rework consumes constrained capacity, so yield improvement often delivers more usable output than capital equipment.
- Low first pass yield in aerospace and defense triggers additional documentation, disposition, and customer notification burden beyond the direct cost.
In Practice
A board assembly line reports 98.5 percent final yield and management considers quality solved. Serialized test data shows 1,000 boards entering, 848 passing test on the first attempt, 137 passing after debug and repair, and 15 scrapped. First pass yield is 84.8 percent, not 98.5 percent. The 137 repaired boards each consumed roughly 25 minutes of technician time, about 57 hours per 1,000 boards, which is the equivalent of a dedicated headcount that never appeared in the yield report.
Frequently Asked Questions
What is the difference between first pass yield and rolled throughput yield?
First pass yield is measured at a single process step. Rolled throughput yield multiplies the first pass yields of every step in a sequence to give the probability that a unit passes the entire routing with no rework at any point. Rolled yield is always lower and is the number that reflects real customer and capacity impact.
Should reworked units count as passing?
Not for first pass yield. That is the whole point of the metric. Reworked units count as first pass failures even when they ship as conforming product, because the rework consumed labor, capacity, and inspection that a right-first-time unit would not have. Count them as passes and you are measuring final yield, which hides the loss.
Related Terms
Rework
Rework is action taken on nonconforming product to bring it into full conformance with the original specification. It differs from repair, which makes product acceptable for use without meeting the original requirement.
Scrap Rate
Scrap rate is the percentage of production output discarded as unusable because it cannot be economically reworked to specification, calculated as scrapped units divided by total units produced over a defined period.
OEE (Overall Equipment Effectiveness)
OEE (Overall Equipment Effectiveness) is a manufacturing metric that multiplies Availability, Performance, and Quality into a single percentage showing how much of scheduled production time an asset spends making good parts at its rated speed.
Go Deeper
OEE Calculator (Overall Equipment Effectiveness)
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