Start with the question
Before scenario assumptions, write the decision question in one sentence. Name who needs the answer, when they need it and which options are on the table. Starting with a report format before the question often creates volume without usefulness.
Separate data from assumptions
For each input, record the source, period and owner, and mark what remains assumed. If two teams disagree, capture the reason and a way to resolve it rather than averaging the disagreement away.
Design the comparison
Use a base case and a few reasoned alternatives, changing the most important variables deliberately. Connect the comparison to separate initial and ongoing effects and show unknowns alongside it.
Review and revise
Set a cadence for revisiting assumptions. When new information arrives, record what changed, why and who confirmed it. A useful review helps the team learn even when actuals differ from plan.
Limits of this article
This is a general planning framework, not case-specific accounting, legal, tax or investment advice.