What-if analysis

What-if analysis changes one or more inputs in a model, a growth rate, a price, a headcount plan, and recalculates the output to show the specific effect of that change, answering a direct question such as what happens to margin if raw material costs rise 10 percent. It is typically interactive, letting a user adjust an input and see the result update immediately.

This differs from scenario planning, which bundles many assumptions together into a small number of coherent, named futures; what-if analysis is more granular and exploratory, often used to test a single lever or stress-test a specific assumption within an existing forecast. It also differs from Monte Carlo simulation, which samples across a full range of uncertain inputs automatically rather than requiring the user to pick each value to test by hand. It commonly runs on top of a driver-based planning model, where inputs and outputs are already linked through defined formulas.

What-if analysis matters because it makes the mechanics of a forecast transparent and lets decision-makers pressure-test assumptions before committing to a plan, often as part of a rolling forecast cycle. The main pitfall is changing one input in isolation when, in reality, that input is correlated with others, producing a technically correct but practically unrealistic result.