There are five methodologies most frequently used:
1. Top down according to budget
2. WBS (Work Breakdown Structure)
3. Guess and gut feeling
4. Early project data
5. TPA (Test Point Analysis)

TPA is a technique used to estimate test efforts for black box testing. Inputs for TPA are the counts derived from function points.

Below are the features of TPA:
• Used to estimate only black box testing.
• Require function points as inputs.

Software applications are a combination of elementary processes. When elementary processes come together they form a software application.

There are two types of elementary processes:

The testing estimates derived from function points are actually the estimates for white box testing. So in the following figure the man days are actually the estimates for white box testing of the project. It does not take into account black box testing estimation.

• File Type References (FTRs): An FTR is a file or data referenced by a transaction. An FTR should be an ILF or EIF. So count each ILF or EIF read during the process. If the EP is maintained as an ILF then count that as an FTR. So by default you will always have one FTR in any EP.
• Internal Logical Files (ILFs): ILFs are logically related data from a user's point of view. They reside in the internal application boundary and are maintained through the elementary process of the application.ILFs can have a maintenance screen but not always.
• External Interface Files (EIFs): EIFs reside in the external application boundary. EIFs are used only for reference purposes and are not maintained by internal applications. EIFs are maintained by external applications.
• External Input (EI): EIs are dynamic elementary processes in which data is received from the external application boundary. Example: User interaction screens, when data comes from the User Interface to the Internal Application.
• External Output (EO): EOs are dynamic elementary processes in which derived data crosses from the internal application boundary to the external application boundary.
• External Inquiry (EQ): An EQ is a dynamic elementary process in which result data is retrieved from one or more ILF or EIF. In this EP some input requests have to enter the application boundary. Output results exits the application boundary.
• General System Characteristics (GSCs): This section is the most important section. All the previously discussed sections relate only to applications. But there are other things also to be considered while making software, such as are you going to make it an N-Tier application, what's the performance level the user is expecting, etc. These other factors are called GSCs.