The unfair verdict a static budget hands down
In the last two guides you built a master budget — that interlocking stack of sales, production, and cash plans that begins with a forecast of how many units you expect to sell and flows all the way down to a budgeted income statement. A budget built that way is a static budget: it is locked to one assumed level of activity, the volume you guessed at the start of the year. Every number in it — materials, labour, packaging, even some overhead — was sized for *that* volume and no other. That is exactly what you want for planning. It becomes treacherous the moment you use it to grade performance.
Here is the trap, told as a tiny story. A workshop budgeted to make and sell 1,000 lamps this month, with variable costs planned at 30 per lamp — 30,000 in total — plus fixed costs of 20,000. The month ends and the production manager has spent 36,000 on variable costs. On a static-budget comparison that is 6,000 *over* budget, an unfavourable variance that lands on her desk like a verdict. But read the rest of the month: demand was strong and the workshop actually sold 1,200 lamps, not 1,000. Of course variable costs rose — there were 200 more lamps to build. Blaming her for spending more to make more is like scolding a chef for buying extra eggs the night a hundred unexpected guests arrived.
The flaw is not in the manager and not even in the budget — it is in the *comparison*. The static budget describes a 1,000-lamp month; the actual results describe a 1,200-lamp month. Setting one against the other compares two different worlds and pins the difference on whoever is standing nearest. To judge fairly we need a yardstick measured at the volume that actually happened. That yardstick is the flexible budget.
Rebuilding the budget for the volume that actually happened
A flexible budget answers a single, honest question: *given the volume we actually reached, what should our costs have been?* It is not a forecast and not a second guess — it is the original plan's own cost assumptions, re-applied to the real number of units. The machinery that makes it possible is something you already met: the split of costs by behaviour into fixed and variable parts. Variable costs are flexed — recomputed at the same per-unit rate for the new quantity — while fixed costs are held exactly where the static budget put them, because by definition they do not move with volume inside the relevant range.
- Take the actual volume that occurred — here, 1,200 lamps. Not the budgeted 1,000; the real number that the period actually produced and sold.
- Flex every variable cost: multiply its original per-unit budget rate by the actual volume. Lamps: 30 per unit × 1,200 = 36,000 of budgeted variable cost for this volume.
- Hold every fixed cost unchanged at its static-budget figure: 20,000 stays 20,000, because building 200 more lamps did not need a bigger building.
- Lay the flexible budget beside the actual results — same volume on both sides now — and any remaining gap is a fair measure of how well costs were managed.
Splitting the gap into two honest pieces
With three columns now in hand — static budget, flexible budget, and actual results — the single misleading static-budget gap breaks cleanly into two meaningful pieces. The distance between the *static* budget and the *flexible* budget is the sales volume variance: it captures everything that changed purely because volume differed from plan. It has nothing to do with cost control and everything to do with selling more or fewer units than forecast. The distance between the *flexible* budget and the *actual* results is the flexible-budget variance: with volume now held identical on both sides, this is the clean measure of whether each unit cost more or less than it should have.
THE LAMP WORKSHOP, ONE MONTH (volume in parentheses)
STATIC FLEXIBLE ACTUAL
BUDGET BUDGET RESULTS
(1,000) (1,200) (1,200)
Variable costs 30,000 36,000 36,000
Fixed costs 20,000 20,000 21,000
Total costs 50,000 56,000 57,000
Static-budget gap (variable costs): 30,000 -> 36,000 = 6,000 U
...which splits into:
Sales volume variance 30,000 -> 36,000 = 6,000 U (pure volume)
Flexible-budget variance 36,000 -> 36,000 = 0 (cost control)
Fixed costs tell a different story:
Sales volume variance 20,000 -> 20,000 = 0 (fixed = flat)
Flexible-budget variance 20,000 -> 21,000 = 1,000 U (overspend)
U = unfavourable (actual cost above budget)Read the table slowly and the manager's verdict reverses. Of the original 6,000 'overspend' on variable costs, every cent is sales volume variance: the flexible-budget variance for variable costs is zero, meaning each of the 1,200 lamps cost exactly the planned 30. She controlled cost per unit flawlessly. The static budget had framed a *triumph of demand* as a *failure of thrift*. The genuinely controllable problem hides elsewhere — in the fixed costs, which came in 1,000 over their flat 20,000 budget. Volume cannot explain that, because fixed costs do not flex; that 1,000 is a real flexible-budget variance worth a conversation.
Reading the two variances like a manager
The two variances answer two different questions and belong on two different desks — which is the heart of responsibility accounting. The sales volume variance asks *did we sell the quantity we planned?* and points toward the sales and marketing side: it is favourable when demand beats the forecast and unfavourable when it falls short, regardless of how tightly the factory ran. The flexible-budget variance asks *did each unit cost what it should have?* and points toward operations: it is the production manager's true scorecard, blind to volume, sensitive only to prices paid and quantities used per unit.
It helps to read the variances on the contribution side too, not just costs. When volume beats plan, the sales volume variance on profit is the extra units multiplied by the budgeted contribution margin per unit — those 200 surplus lamps each threw their planned margin onto the pile. That is why the same volume swing shows up as 'unfavourable' on a variable-cost line yet 'favourable' on the profit line: more units cost more to build, yes, but they earn more than they cost. Naming a variance favourable or unfavourable always means *relative to budget*, never *good* or *bad* in plain English — a 'favourable' cost variance can still mean you skimped on quality, and an 'unfavourable' one can mean you wisely paid up for a rush order that saved a customer.
Where the flexible budget stops, and where you go next
Be honest about the flexible budget's limits, because they are the doorway to the rest of this rung. The flexible-budget variance tells you *that* a unit cost more than planned, but not *why*. Was it that you paid a higher price for materials, or that you used more material per lamp? Those are two very different stories — one a purchasing problem, the other a production problem — and the single flexible-budget variance blends them together. Prising them apart into a price piece and a quantity piece is the job of variance analysis built on standard costs, which the next guides take up in earnest.
One more honest caveat: the flexible budget is only as trustworthy as the cost behaviour it rests on. It assumes the per-unit variable rate and the lump of fixed cost both hold across the gap between budgeted and actual volume — which is true only inside the relevant range. If demand had surged to 3,000 lamps, the workshop would have needed a second shift, more equipment, perhaps a bigger lease; the fixed costs would have jumped to a new plateau and the 30-per-unit variable rate might have shifted too. Flex within reason and the budget is a fair judge; flex it wildly past the range it was built for and you are once again comparing two different worlds.