Budgeting and Forecasting: Testing the Drivers Behind the Plan

Give the approved budget and forecast separate roles

Preserve the approved budget as the recorded plan against which results are explained. Maintain a dated forecast of the outcome now expected, with an assumption log showing what changed. Updating the outlook should leave the original decision visible. This also allows management to distinguish an unrealistic assumption from an execution problem.

ACCA's discussion of rolling budgets describes adding a new period as an old one expires and revisiting assumptions more frequently. It also identifies practical costs: preparation effort, data integrity and disputes over changing performance targets. Choose a manageable update cycle and state explicitly whether a revision changes expected results, authorised spending or performance targets.

Create a transparent operating model

Use a small set of drivers that can be checked against operational records: units delivered, net selling price, variable cost per unit and fixed operating cost. Reconcile the starting point to the management accounts. Identify rebates, returns, one-off items and costs that change only when capacity crosses a threshold.

The following original illustration is fictional, uses currency units and excludes interest and tax. Assume 2,000 units sold at 120 each, variable cost of 70 per unit and fixed operating costs of 60,000. Revenue is 240,000, variable costs are 140,000 and operating profit is 40,000. For this exercise, all units are sold in the period, unit economics are constant and there are no inventory changes.

Explain the variance before changing the outlook

Suppose actual volume is 1,900 units, the selling price is 118, variable cost is 72 and fixed costs are 62,000. Actual operating profit is 25,400: 1,900 multiplied by the 46 unit contribution, less 62,000. The decline from budget is 14,600.

A bridge reconciles that decline: 100 fewer units at the original 50 contribution reduces profit by 5,000; a two-unit price reduction across 1,900 units reduces it by 3,800; two more units of variable cost adds another 3,800 reduction; and fixed costs contribute 2,000. Check the commercial explanation for each movement before carrying it into future periods. A delayed order, temporary discount and permanent supplier increase require different forecast treatments.

Use sensitivities to isolate the important assumptions

ICAEW's financial-modelling guidance distinguishes sensitivity analysis, which isolates specified changes, from scenarios that move multiple inputs together. For the original 40,000 budget profit, test each change independently while holding other assumptions constant. The ranges below are illustrative choices, not market forecasts.

• Volume falls 10% to 1,800 units: profit becomes 1,800 multiplied by 50, less 60,000, or 30,000. A 10% sales-volume decline produces a 25% profit decline.
• Selling price falls 5% to 114: profit becomes 2,000 multiplied by 44, less 60,000, or 28,000.
• Variable cost rises 5% to 73.50: profit becomes 2,000 multiplied by 46.50, less 60,000, or 33,000.

Combine related movements into a coherent scenario

Now assume weaker demand reduces volume to 1,700, discounting lowers price to 114, variable cost reaches 73 and fixed costs rise to 65,000. The combined operating profit is 4,700: 1,700 multiplied by 41, less 65,000. At those unit economics, covering fixed costs requires approximately 1,586 whole units. The calculation illustrates limited remaining room for another adverse change.

ICAEW's board guidance recommends defining who will use scenarios, for which decision and when. For a fictional capacity decision, management could compare delaying expansion, renegotiating delivery commitments and retaining the original timetable. Include implementation costs and operational consequences. Carry each scenario into the cash forecast: operating profit alone does not establish when receipts arrive or commitments must be paid.

State the limits and the resulting management outputs

These simple calculations assume linear costs within available capacity. Overtime, minimum purchase quantities, customer losses and capacity additions can change the relationships. Sensitivity results do not give probabilities, and a downside case is not a guaranteed worst outcome. Choose ranges using documented business evidence and explain omissions.

The resulting pack should contain a reconciled profit bridge, dated driver assumptions, separate sensitivities, coherent scenarios and cash consequences. Add decision thresholds, an accountable owner and an observable trigger for each response. For example, a confirmed order deferral could initiate a capacity review before the next equipment commitment becomes binding.