Six steps are necessary for determining the size of the enhancement expressed in enhancement function points:

The analysis is primarily concerned with determining the FPA user functions which are added, modified or deleted. For this part of the analysis Function Point Analysis (FPA) is used. The result is a summary of the impacted FPA user functions with their functional size.

During enhancement, user transactions and logical data files can be added, modified or deleted. With regard to deleted user transactions and logical data files, the number of function points before deletion is decisive; for added and modified user transactions and logical data files, the number of function points after modification is decisive. The impact of an enhancement may go beyond what is initially apparent from the enhancement proposal. For example, the change of a logical file or transaction may impact other transactions or logical files.

After this, every impacted function needs to be carefully assessed to identify the extent of the impact of enhancement on the function. The impact factor reflects the degree of change of each identified (data and transactional) function.

Finally, the enhancement size of each affected transactional and data function is calculated by multiplying its base size by its impact factor. The enhancement size is measured in “Enhancement Function Points” (EFP), not standard function points, which is a different measure. It is imperative to maintain the distinction between the standard function point unit used to express the size of software (FP) and the unit used to express the size of an enhancement (EFP). In the following chapters, the relationship between the original and the new unit of measure will be described.