A business case is easiest to defend before work starts, when estimates are optimistic and the proposed benefits have not yet been tested. Its value grows when the project encounters real costs, delays or changed priorities. At that point it should support a decision, not simply justify a decision already made.

Separate outputs from benefits

An output is what the project delivers. A benefit is a measurable improvement that follows from using the output. A fictional organisation introducing a document-management system might expect faster retrieval of records. Installing the software does not establish that benefit; staff must use it and retrieval performance must be assessed.

Assign responsibility for benefit measurement. Record a baseline where possible, the expected improvement and the point at which a meaningful review can take place. Some benefits will only be measurable after the project closes.

Revisit assumptions when evidence changes

A supplier estimate can change. A regulation can alter the required solution. A user group can discover that an assumption was wrong. Review the effect on the investment rather than treating each change as an isolated scheduling problem.

Continued business justification is a PRINCE2 principle. A project should remain desirable, viable and achievable as it progresses. Approval at the beginning does not remove the need to check those conditions later.

Make the decision visible

When the case changes, present the available options with their consequences. Continuing, changing scope, delaying work or stopping can all be legitimate choices. The appropriate choice depends on the evidence and the authority of the decision-maker.

A useful business case makes trade-offs understandable. It should not hide uncertainty behind precise-looking figures or imply that the team must continue simply because money has already been spent.