Changing one input of a plan or forecast at a time to see how far the result moves.
Sensitivity analysis tests how much a result, such as profit, cash or a target, depends on each input. Move one input by a set amount, hold the others at base, and record the change. It finds the inputs worth arguing about. Scenario analysis differs: it moves several inputs together into a coherent story.
Result at changed input − result at base, for each input in turn, often in a grid of steps such as −10%, −5%, +5% and +10%. In Excel a one- or two-variable data table does the recalculation.
A base plan sells 10,000 units at $50 with a $30 variable cost per unit and $150,000 of fixed costs: revenue $500,000, profit $50,000. Cut price by 5% to $47.50 and revenue falls to $475,000, so profit falls to $25,000. A 5% price move halves profit.
Moving inputs that in practice move together, such as volume and price, one at a time. Using symmetric steps for inputs that can only fall. The full guide is scenario analysis in Excel.