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.
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.
The same example using first pass yield (FPY) would take into account rework: (# units leaving process A as good parts with no rework) / (# units put into the process) 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.