S-curves, a picture is worth a thousand
what the mysterious S Curve is, why it is an important project
management tool, and how to generate one.
WHAT IS AN S CURVE ?
"a display of cumulative costs, labour hours or other quantities plotted against time.
The name derives from the S-like shape of the curve, flatter at the beginning & end,
and steeper in the middle, which is typical of most projects. The beginning represents
a slow, deliberate but accelerating start, while the end represents a deceleration as
the work runs out."
TYPES OF S CURVE ?
There are a variety of S Curves that are applicable to project management
Man Hours versus Time S Curve
Cost versus Time S Curve
Baseline S Curve
Actual S Curve
MAN HOURS VERSUS TIME S CURVE
The Man Hours versus Time S Curve is appropriate for projects that are labour
intensive. It shows cumulative man hours expended over time for the duration of
the project. As man hours are a product of man power and working hours, these
may be adjusted individually or together to ensure the project remains on schedule
COST VERSUS TIME S CURVE
The Cost versus Time S Curve is appropriate for projects that contain labour and
non-labour (e.g. material supply / hire) tasks. It shows cumulative costs expended
over time for the duration of the project, and may be used to assist in the
calculation of the project's cashflow.
BASELINE S CURVE
Prior to project commencement, a schedule is prepared outlining the proposed
allocation of resources and the timing of tasks necessary to complete the project
within a set time frame and budget. This original schedule is referred to as the
Baseline Schedule. From this schedule, a Baseline S Curve is generated. This S
Curve reflects the planned progress of the project.
TARGET S CURVE
ACTUAL S CURVE
The production schedule is updated on a regular basis throughout the duration
of the project. These updates include the revision of percentage complete for
each task to date. Using this information, an Actual S Curve may be generated.
This S Curve reflects the actual progress of the project to date, and may be
compared with the Baseline S Curve to determine how the project is
VALUE AND PERCENTAGE S CURVES
S Curves are useful for calculating the project's actual percentage complete
against baseline percentage complete, and for calculating the project's
percentage growth (or shrinkage).
WHY USE A S CURVE?
an important project management tool.
allow the progress of a project to be tracked visually over time,
form a historical record of what has happened to date.
allow project managers to quickly identify
o project growth
o potential problems
that could adversely impact the project if no remedial action is taken.
Comparison of the Baseline S Curve and Actual S Curve reveals the progress of
the project over time. In most cases, the Actual S Curve will sit below the
Baseline S Curve for the majority of the project (due to many factors). Only
towards the end of the project will the curves converge and finally meet. If the
project is ahead of schedule, the Actual S Curve will rise above the Baseline S
HOW IS A S CURVE GENERATED ?
In order to generate a S Curve , a Baseline and Production Schedule are required.
These schedules should contain the following information for each task...
Baseline / Actual Start Date, Finish Date
Baseline / Actual Man Hours, Costs
Actual Percentage Complete
S Curves may be used by Project Managers to track the progress of their Projects.
Graphical tracking allows the quick and timely identification of potential problems
that could adversely affect the progress of the Project.
S Curves may also be included in the routine Progress Reports required by Senior