Project Duration
Project duration is the measure of the elapsed months that a project is completed in.
As with most aspects of the software development process, software duration has many influencing factors.
Functional Size and Duration Relationships
You can estimate project duration using your estimation of software size, your software development life cycle phase profile, (including overlap between phases and activities), staff availability and other factors.
For a "ball park" or indicative estimate of duration, several "rules of thumb" equations, or quick estimating techniques are available. Two are shown below.
Functional Size and Duration
Analysis of data from the ISBSG repository has produced a detailed set of equations that you can use to achieve indicative estimates of project duration. Appendix 3 of the Practical Project Estimation 2nd edition contains a complete set of the equations. Here are three examples of duration estimates using the ISBSG equations:
For a project of 500 Function Points using the language only equation table:
| Project Class | Equation | Project Duration - Months |
| 3GL projects: | Duration = 0.971* 500^ 0.351 | 8.60 months |
| 4GL projects: | Duration = 0.622 * 500 ^0.405 | 7.71 months |
| Application Generator | Duration = 1.472 * 500 ^0.280 | 8.39 months |
Interestingly, work by Capers Jones provides a similar 'rule-of-thumb' equation:
Duration = FPSize
where Duration is in Calendar Months.
eg., for a project of 500 Function Points,
Duration = 7.93 calendar months.
Finding similar results drawn from two sets of data collected in entirely different ways, lends support to the notion that, in general, there is a predictable relationship between the functional size of a Program(s) and the duration of the project to produce the program(s).
Work Effort and Duration Relationship
An analysis of 662 projects in the ISBSG repository that reported their project duration, the following equation was produced:
Duration (calendar months) = 0.38 * Effort ^0.37
You can create an Excel formula to use this equation: =SUM(0.38*(effort^0.37))
The above "rule of thumb" equations are useful as a first indication of possible project duration. Of course, other factors such as the availability of resources and the business environment, must always be kept in mind. These additional factors should be used to apply judgement before drawing conclusions from the values calculated using any of the equations above.
Team Size and Duration Relationship
Project Managers are often faced with the task of providing information about the likely size, cost and duration of a proposed project to assist with a business decision about the project's feasibility. As part of this task they often seek answers to the following questions:
- Is it practical, or possible, to deliver software of the estimated project size within the target time frame?
- What effect will the project team size have on productivity?
- If I have an available team size of 'n' people, what is the likely elapsed time for the project?
The Software Metrics Compendium presents the results of investigations into the relationship between Team Size and Project Delivery Rate (productivity). | "The Special Reports in particular are a good source of practical
information that we use to broaden our understanding of current issues and compare performance, often arriving
just at the right time!"
Carol Drummond
BT EXACT
British Telecommunications
"The wealth of data and processed information in the form of reports, provide real insight into IT industry's performance levels. We use this information to better our project estimates at time of bidding. It provides sound logic and convincing reasons to both internal and external stakeholders."
Alok Sharma
CSC India Pvt Limited
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