The problem with all project planning is that you cannot foresee or totally control the future. If you could, projects would be easy. But you can't, so all you can do is project into the future with greater or lesser accuracy. The more knowledgeable you are about the durations of your deliverables and the risks associated with your schedule, the more accurate your schedule will be.
In addition, our ability to predict the future diminishes as we try to project further out into the future. Therefore, shorter schedules tend to be more accurate than long ones.
Because there is always uncertainty when you project into the future or attempt to estimate durations, you should add some contingency to the end of the schedule to cover the uncertainties. Contingency is like an insurance policy. You may not need it, but it's better to have it so that, when Murphy's Law hits, you have a savings account of time to help protect your deadline date.
There is no magic formula for how much contingency you'll need. It will depend on these factors:
✓ The complexity of the project. The more complex the project, the more contingency you'll probably need.
✓ The amount of risk in the project. The more risk, the more contingency.
✓ The length of the project. Longer projects require more contingency because it gets harder and harder to predict the future.
✓ If you've done this type of project in the past, you'll need less contingency than if this type of project is new to the project team.
✓ The experience of the team. More experienced teams require less contingency because they are better at estimating.
✓ The amount and accuracy of historical data available from similar projects. If you have accurate data, then your estimates will be closer to reality and you'll need less contingency.
✓ The reliability of vendors. The more unreliable, the more contingency you'll need.
✓ Degree you must share resources with other projects. This creates greater uncertainty in the duration estimates and increases the risk that team members will be pulled off your project to work on other projects.
How much contingency is enough? That's something you'll also have to guess. Until you have good historical data, you're better off adding more than you think you need.
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What you need to know about… Project Management Made Easy! Project management consists of more than just a large building project and can encompass small projects as well. No matter what the size of your project, you need to have some sort of project management. How you manage your project has everything to do with its outcome.