The 20 - percent solution

how to stop playing games with your project schedule


By Ronald B. Smith, PMP

MOST RECENTLY BASELINED project plans are inaccurate because they have unrealistic start dates, finish dates, work hours, costs and/or durations. Poor estimating during the planning phase is a big contributor to project failures.

However, project managers can build more accuracy and credibility into their project plans by incorporating the 20-percent solution into three areas.


No one is available to work on projects 100 percent of his or her time—people take breaks, attend meetings, get stuck in traffic and so on. Therefore, you should make the assumption a resource is unavailable 20 percent of the time and available 80 percent. If a resource is available only half-time for a project, set the maximum units of availability at 40 percent. Also remember to include holidays, plant shutdowns, training and individual resource vacations when setting up your project's schedule.

No plan ever runs according to schedule. Some tasks will come in late, so you need some wiggle room.


No plan ever runs according to schedule.

Some tasks will come in late, so you need some wiggle room. A good idea is to add a buffer task at the end of selected phases (for example, phases involving new technology that your team has limited or no experience using) or to extend the project's summary end date for that phase by 20 percent from its original duration. For example, if the original phase duration is 100 days, extend it to 120 days.

If you don't end up using the entire buffer, reduce the buffer's duration time to get an accurate project completion date. If you don't use any of the buffer, delete or inactivate it (remove the values from your rolled-up schedule). In this situation, I recommend inactivating the task so it is saved for historical reasons and can be reactivated later if needed for an emergency.


Since organizations usually don't spend enough time on risk management, contingency funds totaling 20 percent of the total budget should be set up for each project.

There are two types of risks. Known unknowns are identified at the beginning of the project, and unknown unknowns are identified during the execution of the project. Set up contingency funds of 10 percent of the budget for each of these risk categories. These safety margins should obviate the need for padding task estimates (probably the worst habit a project manager can develop) and similar games, and help to produce an honest project plan that will get stakeholder buy-in.

Following these three tips should improve your project plan's credibility and performance. If you discover over time and through lessons learned that the 20-percent figure is not appropriate for your organization, adjust to what works best (for example, 17.5 percent or 25 percent). PM

img Ronald B. Smith, PMP, recently retired from IBM Global Services and now teaches project management to technical graduate students at the University of Houston, Houston, Texas, USA.




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