First pass yield

First pass yield (FPY), also known as throughput yield (TPY), is defined as the number of units coming out of a process divided by the number of units going into that process over a specified period of time. 
Example.
Consider the following:
You have a process that is divided into four sub-processes: A, B, C and D. Assume that you have 100 units entering process A. To calculate first time yield (FTY) you would:
For example:
(# units leaving the process as good parts) / (# units put into the process) = FTY
The total first time yield is equal to FTYofA * FTYofB * FTYofC * FTYofD or 0.9000 * 0.8889 * 0.9375 * 0.9333 = 0.7000.
You can also get the total process yield for the entire process by simply dividing the number of good units produced by the number going into the start of the process. In this case, 70/100 = 0.70 or 70% yield.
The same example using first pass yield (FPY) would take into account rework:
First pass yield is only used for an individual sub-process. Multiplying the set of processes would give you Rolling throughput yield (RTY). RTY is equal to FPYofA * FPYofB * FPYofC * FPYofD = 0.8500 * 0.8889 * 0.8125 * 0.8267 = 0.5075
Notice that the number of units going into each next process does not change from the original example, as that number of good units did, indeed, enter the next process. Yet the number of FPY units of each process counts only those that made it through the process as good parts that needed no rework to be good parts. The calculation of RTY, rolling throughput yield, shows how good the overall set of processes is at producing good overall output without having to rework units.