This paper was originally authored by Greg Gendall of Midori Media and published by Project Magazine in May 2003. It has since been revised and updated by the present author. It was submitted for publication by Email, February 16, 2009, and is copyright © David Garland. Published here May 2009.

Generating S-curves

Project Benchmarks

Percentage S-curves may be used to calculate important project benchmarks on an ongoing basis, including:

• Project percentage growth (Target and Baseline S-curves)
• Project percentage slippage (Target and Baseline S-curves)
• Actual percentage complete against Target percentage complete to date
• Actual percentage complete against Baseline percentage complete to date

How is an S-curve Generated?

To generate a Baseline S-curve, a Baseline Schedule is required.
The Baseline Schedules should contain the following information for each task:

• Baseline Start Date, Finish Date
• Baseline Man Hours and/or Costs

To generate Actual and Target S-curves, a Production Schedule is required.
The Production Schedules should contain the following information for each task:

• Actual Start Date, Finish Date
• Actual Man Hours and/or Costs
• Actual Percentage Complete

Worked Example

To better understand how S-curves are generated, consider a simple project comprising three tasks.
A Baseline Schedule prepared using MS Project for this project is shown below.

Baseline Man Hours versus Time S-curve

To generate a Baseline Man Hours versus Time S-curve, two sets of calculations are performed.
The first set of calculations is performed for each task in the Baseline Schedule.

1. Calculate the duration in days for each task
i.e. Baseline Duration = Baseline Finish Date - Baseline Start Date + 1
2. Calculate Man Hours per day for each task
i.e. Baseline MHs per Day = Baseline Man Hours / Baseline Duration

These calculations are shown in the following table.

Figure 10: Baseline S-curve Calculation 1 of 2

The second set of calculations is performed for each day in the Baseline Schedule.

1. Calculate the total Man Hours per Day for all tasks.
2. Calculate the Year To Date Total for Man Hours per Day for all tasks.

These calculations are shown in the following table.

Figure 11: Baseline S-curve Calculation 2 of 2

The S-curve is constructed by assigning the Dates to the X Axis, and the YTD values to the Y Axis.
The resulting Baseline Man Hours versus Time S-curve is shown below.