What are project assumptions and why should you care about them?

I’m not gonna lie to you: This article was hard to write because it’s such a dry topic. But still, I believe you should be aware of the role assumptions have in projects. And understanding their impact will help you avoid some common project risks.

So let’s look at what project assumptions are and why they deserve your attention.

What are project assumptions?

Project assumptions are certain things we consider to be true which impact the way we plan or manage a project (see PMI definition). We consider those factors to be true in order to give us a basis for planning. If we couldn’t be sure about anything, we could not make any predictions about the duration and cost of our project.

Assumptions may concern various areas, including our own role and responsibilities, our client’s responsibilities, legal regulations, the client’s needs as well as future events that we expect to take place.

Hell, this was a lot of abstract babbling.

Let’s make things clear with a few practical examples:

Practical examples of project assumptions

You’ll best understand the concept of assumptions by these examples:

  • Assumptions about skills: You are discussing an IT system replacement project with a potential client. The client’s CIO tells you they have a “very experienced” IT team who has done “hundreds of migrations”. You therefore agree with the client that they are going to perform the data migration themselves. The client is happy that they can save cost.
  • Scheduling assumptions: Your project team members are also involved in another project. Therefore you’ve planned key activities (e.g. business trips) so that they don’t collide with the other project. For your planning and resource allocation you assume that the other project will follow its original schedule.
  • Cost assumptions: For a construction project you are purchasing 5 tons of cement in May, and you’re going to buy the same quantity again in October. You assume that the cement price is going to remain stable over the next months.
  • Assumptions about the legal environment: To make your client an attractive offer, you are planning to hire foreign temporary workers from India to work at the client’s office for a couple of months. According to current labor and immigration laws this is possible. You assume that the legal rules will remain the same over the course of this 24-month project, and this is reflected in your project plan and budget which are based on the lower labor cost.

Why project assumptions are ticking time bombs

Going through the examples, you probably noticed the issue with assumptions: If they turn out to be wrong or if the environment changes, your project can get into serious trouble.

Take the above example of hiring foreign workers:

  • You assumed that (cheaper) external staff are going to perform the work. Hence, your cost estimations are much lower than in a scenario involving domestic workers. If the government now decides to ban foreign temporary workers, you have a big problem.
  • You’ll have to deliver to the client, but you’ll have to use (more expensive) domestic staff which make 3-5x more than workers from India. In the end, you’ll make a loss on the project. If you are a big company this won’t hurt you much. But if you are a small contractor, even one such project can end your business.

Exploding cost is just one of the consequences of basing work on invalid assumptions. In other cases the project scope may explode (this is what’s called scope creep) or the project may run into a severe delay.

Read my tips on how you can avoid project delays

Spot assumptions before they cause trouble

Takeaway from this article: Be aware of assumptions and the problems they can cause in projects. Always challenge assumptions made by others, and be conscious about the assumptions you make yourself (this is even harder). It takes some skill and practice to notice when people make assumptions, but asking for evidence for an idea or statement is always a good starting point to uncover potential assumptions.

Finally, I want to point you to one technique that is helpful for identifying assumptions. It is to create an assumptions list together with your project team — basically a brainstorming session with the people involved.


  • Adrian Neumeyer

    Hi! I’m Adrian, founder of Tactical Project Manager and Ex-Project Manager with over ten years of experience in project management. Led large-scale IT implementations and business projects. I started Tactical Project Manager to offer you a straightforward and pragmatic approach to project management, enabling you to lead any project with confidence.

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