In a project management language, an assumption is an “event” with a probability of over 50%. If the probability of the event is also less than 100%, it is a risk!!!

An assumption is something that you assume to be the case, even without proof.

While there is a clear relationship between assumptions and risks, they have different point of view:

  •  If the risk event happens then, the project is affected.
  •  If the assumption event doesn’t happen, then the project is affected.



We assume that critical resources are going to be available when required.


If the critical resources are NOT available when required, then there is a certain event that will cause an impact.

Key Points to Remember:

  • Risk associated with an assumption (as any other type of risk) has a probability and an impact.
  • Risk associated with the assumption has low (<50%) probability. However, it doesn’t mean that impact is also low.
  • Some of the assumptions may have 100% probability. In this case, these are facts, not risks. It is still important to document them if there is a chance that not all project stakeholders are aware of these facts.
  • Unless it is possible to prove that an assumption is a fact, it is better to assume that it is a risk.
  • Assumptions could be managed in a risk register or in an assumption register. In that case, two registers need to be integrated.
  • Risks with low probability and low impact often have “Accept” mitigation strategy. Assumptions are also often just accepted and don’t have a mitigation plan. However, if the risk associated with an assumption has a medium or high impact, the “Accept” mitigation strategy may not the best mitigation strategy.
  • A risk associated with an assumption also may have a positive effect. In this case, it is an opportunity:
  • If the threat event happens then, the project is negatively affected.
  • If the opportunity event happens, the project is positively affected.
  • If the assumption event doesn’t happen, then the project is positively or negatively affected.


We assume that Australian borders are going to be closed till the end of 2021. Opportunity: if borders are opened earlier, we may be able to conduct a conference earlier (in December 2021).

Types of Dangerous Assumptions


Assumptions are made “automatically” by an individual, without even realising it.


Some assumptions could be obvious for someone, and this person doesn’t see a need to communicate this assumption to the rest of the team. Other project stakeholders may not have the same knowledge or information. They would act differently if they would be are aware of these uncommunicated assumptions.


Assumptions that are “pushed” without an open conversation. A project team member may be aware of the high risk associated with this assumption but doesn’t feel comfortable to raise the concerns.

Naive assumptions

Some assumptions are based on lazy or unimaginative thinking.


Pragmatic assumptions that may be obviously untrue but designed to motivate positive behaviour.
The assumption is that the project manager is skilled enough to deliver the project.

Unrecognised & Unstated assumptions are not documented, and project stakeholders are entirely unaware that someone is “making things up”.

Dangerous assumptions may have a high (>50%) probability of risk associated with the assumption!

As a result, the project team could get in a serious trouble , as a proper risk response is not prepared, and risk not mitigated.

Alex Lyaschenko

PMO | Portfolio Planning & Delivery | PMP | P3O Practitioner | AgilePM Practitioner | Six Sigma