An assumption log is a document that a project manager and project team utilize to capture, record, and track assumptions on a project throughout its life cycle. Assumptions play a significant role in every project, and it should be no surprise that an assumption is considered essential information on which project plans and decisions are made.

Assumptions typically require some follow-up or validation to determine whether they will impact the project. An assumption log is created during project initiation, specifically during the formation of the business case and the content that will become part of the project charter. High-level assumptions are used during this stage, and lower-level assumptions are created during the project life cycle.  

Assumptions made throughout the project life cycle may turn out to be project risks, or they may have the potential to become risks during the project's life. Proper risk management is necessarily performed on the project for this very reason. A risk management plan and risk register should be included, and the assumption log should never replace the risk register.

A simple example of an assumption that could be made during a project is the availability of project resources. If the needed resources are unavailable for whatever reason, the delivery of the project is at risk. An assumption log is helpful since it allows the project manager and team to foresee potential project risks and other issues that could hinder a project's productiveness. 

 An assumption log assigns each assumption the following:

• name and description

• category

• owner or person responsible

• date first logged

• due date

• rating for the uncertainty (high/medium/low)

• date for the next review

• level of impact (high/medium/low)

• status - open or closed

• closure date

• action plan that is part of the follow-up or validation

The assumption log requires updating as items are closed or more information is obtained. During an ideal project, the assumption log will be reviewed regularly. Activities will need to be verified so all project team members can remain informed and any additional information can be captured.

Assumptions are prioritized in the assumption log based on the level of uncertainty and the potential impact to the project if the assumption turns out to be incorrect. Assumptions with the highest level of uncertainty and highest potential impact are considered the highest priority.