1. Deadly Sins of Software
Estimation
(modified from sources on the Internet)
Gerrit Klaschke

2. Deadly Sins of Software Estimation
 Sin #1: Estimating how long “it” will take to
build before anyone knows what “it” is.
 Solution: Go through a scope/discovery phase to
determine the project goals and requirements.
 Sin #2: The most reliable estimate comes from
the person with the most powerful vocal chords.
 Solution: After the project has been defined, use
formal estimation methods and tools to determine
effort, schedule, cost etc. for your project.

3. Deadly Sins of Software Estimation
 Sin #3: Don’t account time for vacation time, sick time
etc.
 Solution: use the correct ‘hours per month’ settings in
estimation tools to have a realistic number of hours worked.
Further, mitigate the risk that team members might be called to
work on other projects.
 Sin #4: Compare the new project to a previous project
which was over budget, was late, or used massive
overtime. This will result in a wrong baseline for your
new estimate.
 Solution: Try to compare to a project which actual results were
close to the estimated results. Further, use completed projects
to calibrate the estimation tool you use to ensure optimal results
for your company and environment.

4. Deadly Sins of Software Estimation
 Sin #5: Believing that you don’t need to estimate
because you have not done it in the past.
 Solution: Try an estimation tool and see what it can do for you.
 Sin #6: Confusing targets with estimates. Targets are
sometimes set without doing real estimation first.
 Solution: Complete the project scope/discovery phase and use
an estimation method to create an estimate. If the project end
date is unacceptable for management, try to descope, add more
staff etc. An estimation tool can give you many options to play
‘what if’ scenarios and show you the effect on the schedule.

5. Deadly Sins of Software Estimation
 Sin #7: Committing to estimates too early in the
cone of uncertainty.
 Barry Boehm describes the ‘estimation funnel’: The
precision of your estimate gets greater over time as
you learn more and more about the project.
 Over time you gather requirements, do design and
start development. Re-estimation of the project using
the new available data is paramount to better predict
the remainder of your project.

6. Deadly Sins of Software Estimation
 Sin #8: Estimating in the impossible region.
 Empirical evidence exists to document an impossible
region, beyond which a project schedule cannot be
accelerated simply by throwing money at it.
 Solution: Add team members. Be aware of Brook’s
law though, which says: Any manpower added to a
late project makes it later. This is due to
communication and coordination.

7. Deadly Sins of Software Estimation
 Software estimation is a fundamental part of the
project management methodology (see the
PMBOK).
 Treat estimation as a mini-project and create an
estimate for effort, schedule and cost of the
software project.
 By doing this, the chances of completing the
project successfully are increased substantially.