First pass yield and rolled throughput yield explained

Try it while you read

Open the free First Pass Yield (FPY) Calculator tool and click Load sample: it reproduces the case study below.

Theory: first pass yield and the hidden factory

FPY = units good the first time / units tested

RTY = FPY₁ × FPY₂ × … × FPYₙ

First pass yield measures how many units pass a process step without rework, repair or retest. Rework is often invisible in the scrap figures, but it costs time, capacity and quality risk. This part of the operation is called the hidden factory.

Rolled throughput yield combines the steps of a line: the probability that one unit passes every step the first time. It drops quickly with each step, which is why a line with good single yields can still have a poor RTY.

Target and watch band

Each process gets an FPY target. With a watch band, for example 2 percentage points, the status is OK at or above target, WATCH within the band below target and ACTION below the band. The RTY target is the product of the process targets.

Key point

Improve the weakest step first. Raising a 94 % step to 96 % lifts the RTY more than raising a 98 % step to 99 %.

Step by step

Processes: in the FPY calculator list the steps in flow order with their targets, and set the watch band.
Log: per date, shift and process the units tested, the units good first time and the main defect. Paste from Excel or the MES export.
Period: choose the date range to evaluate.
Read FPY per process with status, the RTY against target, the weakest process, the top defects and the daily trend.
Report: download the PDF or the free FPY Excel template for the shop floor.

Case study: five-step assembly line

The Load sample holds ten days, two shifts and five processes, about 8,000 units per process.

Process	Target	FPY	Rejected	Status
Pre-assembly	97 %	97.4 %	205	OK
Brazing	95 %	93.9 %	495	WATCH
Assembly	96 %	96.6 %	269	OK
Painting	96 %	96.3 %	291	OK
Final test	98 %	98.6 %	112	OK
RTY	83.2 %	83.9 %

The line RTY is slightly above its target, yet brazing is in the watch band and produces the most rejects. The daily trend shows brazing dropping in the second half of the period, and leaks are the top defect. A Pareto of the brazing defects and a check of the brazing temperature profile are the next steps.

Result

The team finds a worn nozzle on the brazing station. After replacement, brazing returns to about 95.5 % and the line RTY rises by about 1.4 points: roughly 13 fewer reworked units per day at brazing, or 130 over the ten days.

Common mistakes

Counting reworked units as good, which makes FPY look like yield.
Averaging FPYs of a line instead of multiplying them into RTY.
One target for all processes regardless of their difficulty.
Looking only at the monthly number and missing a drift within the month.

Turn the rework into money with the COPQ calculator, and look at availability and speed losses with the OEE calculator.

Frequently asked questions

What is the difference between FPY and yield?

Yield usually counts all good parts including reworked ones. FPY counts only the parts that are good the first time, without rework or repair, so it shows the hidden factory of rework.

Why is RTY lower than every single FPY?

Because a unit must pass every step first time. RTY is the product of the FPYs: five steps at 96 % give only about 81.5 %.

What is a good FPY?

It depends on the process. Final test of a mature product is often above 98 %, a complex brazing or painting step may run at 93 to 96 %. Set targets per process from capability and cost, then improve them.