Calculate the contribution cost of a discount campaign
Compare a discount offer with a no-discount baseline using contribution, incentive cost and the incremental order count needed to break even.
What would happen without the discount?
An offer needs a baseline because some customers would buy without it. The discount reduces contribution on those orders too. Counting every discounted order as incremental ignores that cost. Start with an explicit baseline and treat its uncertainty as part of the decision rather than choosing a convenient number after the promotion.
The arithmetic below is an original illustrative USD model. Microsoft documents SUMPRODUCT for summing corresponding products, which can support a multi-product version. The spreadsheet still needs valid prices, variable costs and quantities; the function does not establish the baseline or the offer’s causal effect. [SUMPRODUCT function]
A no-discount and discount comparison
Illustrative inputs: normal price $100, variable fulfillment cost $60 and 100 baseline orders. The proposed discount is 10%, making the offer price $90. Variable cost remains $60 in this simplified scenario, and execution adds $200. These are teaching assumptions, not campaign results or market prices.
| Scenario | Orders | Contribution per order | Execution cost | Total contribution |
|---|---|---|---|---|
| No discount baseline | 100 | $100 − $60 = $40 | $0 | $4,000 |
| Discount, no extra demand | 100 | $90 − $60 = $30 | $200 | $2,800 |
| Discount, break-even volume | 140 | $30 | $200 | $4,000 |
| Discount, higher volume | 160 | $30 | $200 | $4,600 |
To preserve baseline contribution, required discounted orders are ($4,000 + $200) ÷ $30 = 140. That means 40 additional orders, or 40% above the illustrative baseline. The threshold is a planning calculation. It does not establish that demand can increase by that amount.
At 160 orders, contribution after execution cost is 160 × $30 − $200 = $4,600, or $600 above baseline. Revenue has increased too, but contribution is the relevant comparison under this cost boundary. Adding omitted returns, processing or support costs could change the result.
Which costs and behaviors could reverse the decision?
- Discount applies to people who would have paid full price.
- Incremental volume changes fulfillment or support costs.
- Returns, cancellations or payment costs differ under the offer.
- Customers move purchases forward rather than adding demand over a longer window.
- Product mix shifts toward lower-contribution items.
- The baseline forecast is uncertain or affected by another campaign.
A fixed variable-cost assumption is useful for a small teaching model, but real costs can step up when capacity is exceeded. Preserve that boundary. If the discount creates overtime or a new fulfillment tier, model the relevant range instead of multiplying every extra order by an unchanged margin.
How can the offer be evaluated fairly?
Where practical, preassign eligible groups and compare matched observation windows with a clear treatment. Keep outcome definitions and incentive accounting consistent. A before-and-after increase can reflect seasonality or another change, so it should not automatically be attributed to the discount.
The completed worksheet should show the baseline, offer price, cost boundary, threshold and uncertainty. It can support a decision to reject, redesign or test the offer. It cannot guarantee demand, profitability or a universal optimal discount.
Sources
AI-assisted writing and an AI-generated editorial cover. Source links and checked dates are listed below; illustrative examples are labeled in the text.
- SUMPRODUCT function — checked 2026-10-18