Incremental profit formula: revenue less added costs

The incremental profit formula is added revenue minus the relevant costs added by a decision. Compare the business with the decision against the same business without it, over the same period. A proposed order with $57,600 of additional sales and $41,928 of additional costs adds $15,672 of operating profit before tax.

The formula and the comparison it answers

Incremental profit = Revenue with the decision - Revenue without the decision - (Costs with the decision - Costs without the decision)

Equivalently: Incremental profit = Added revenue - Added relevant costs - Contribution lost from displaced business

Use the second expression only when displaced business has not already been included in the revenue and cost differences. Otherwise you would subtract the same loss twice.

The question is specific: should the company accept this order, extend this route, or add this shift? It is different from asking whether the whole company earns an acceptable operating margin. An order can improve profit while carrying a lower percentage margin than existing sales.

OpenStax explains that differential analysis compares the relevant revenues and costs of alternatives. Relevance depends on what changes. A cost described as fixed can matter when the decision creates it; a cost assigned to a product can be irrelevant when it remains unchanged.

Start with the order and cost exports

Build a decision workbook from the proposed order lines, supplier quotes, labor schedule, freight quote, and commission terms. Keep the assumption source beside each amount so finance can distinguish a quoted cost from an estimate.

Classify costs by their behavior in this decision. Existing salaried labor may remain unchanged, while extra hourly labor may rise with production. The gross profit margin calculation uses the company's cost-of-goods-sold policy; it does not make this relevance test for you.

Keep the time horizon explicit. A temporary arrangement may have no added facility cost this month but require leased space if it becomes recurring. Do not extend a short-term conclusion indefinitely.

Worked order: available capacity

Consider an illustrative US manufacturer, Northline Fixture Co. It can fulfill a proposed order without displacing other customers. The order is for 1,200 units at $48 each. Materials, paid production labor, and packaging are incremental; the existing factory lease remains unchanged.

Every calculation below is exact to the cent. Whole-dollar amounts are displayed because each result is a whole dollar.

The assumed tooling is expensed in this decision period. A purchase that must instead be capitalized needs an expense analysis consistent with the reporting period and a separate cash investment appraisal.

Profit added per unit is 15,672 / 1,200 = $13.06. That amount describes this order at this volume; the tooling does not recur with each unit.

Two other figures appear in the costing workbook but do not belong in the added-cost total:

The allocation remains relevant to company-wide cost recovery, but rejecting the order does not save it. The design fee is a sunk cost. Neither exclusion means the company can ignore those expenses in its financial statements.

The proof: reconcile to the operating statement

Northline's monthly baseline has $300,000 of revenue, $180,000 of variable expenses, and $70,000 of fixed expenses. Classify the proposed order's added costs other than tooling as variable for this illustration; put the tooling below contribution.

The check is 65,672 - 50,000 = $15,672, exactly the order calculation. If the two results differ, inspect duplicated expenses, missing setup charges, and costs that were allocated rather than changed.

This is an operating-profit comparison. Interest and taxes require an explicitly broader calculation; gross profit vs net profit explains the accounting levels. Do not label the result net profit simply because all listed order costs have been deducted.

What changes when capacity is full

OpenStax's special-order analysis starts with capacity and considers added resources and fixed costs. The available-capacity assumption is therefore part of the answer, not background detail.

Suppose the same order would now displace 500 regular units, each contributing $35 after its avoidable costs.

The order now reduces operating profit by $1,828. Use lost contribution, not the displaced revenue alone, because the displaced orders also release their variable costs.

Keep sensitivities tied to a changed input. If freight rises from $3,000 to $4,200 with capacity still available, added profit falls by $1,200 to $14,472. A full schedule and a higher freight quote are separate cases; combine them only when both conditions apply.

Where it goes wrong

• Allocations treated as savings. Existing rent assigned to an order does not become avoidable when that order is rejected.
• New fixed costs omitted. Temporary equipment, setup, and supervision can change even when they do not vary per unit.
• Displaced sales counted twice. Include the lost business in the with-versus-without statement or subtract lost contribution separately, once.
• Profit confused with a ratio. Incremental margin divides the profit change by the revenue change. This decision first needs the dollar amount.
• An estimate treated as permission. Finance owns the reconciliation; operations confirms capacity, and sales confirms the commercial terms before approval.

Evaluate your own order in Covirage

Bring a workbook containing the proposed order, baseline expenses, and the costs that would change. Covirage maps the columns, and its tools compute and check the figures; the external AI model explains the result with every figure traced to its rows. Create a free Covirage account and bring a sample of your own data.

See Covirage for finance teams for the supporting financial reporting use case.