# Marketplace Promotion ROI Calculator

> Compare profit with and without a marketplace deal: discounted margin, extra units, promotion fees and ad spend, incremental profit, ROI and break-even units.

Category: Commerce & retail · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/marketplace-promotion-roi-calculator

A promotion pays off only if the extra units at a lower margin earn more than you would have made anyway at full price, after the deal fee and ad spend.

Also called: Deal ROI calculator, Promotion profitability calculator.

## Inputs
- Regular selling price (default 40)
- Promotion discount (unit %; default 20)
- Cost per unit (product + fulfilment) (default 18)
- Marketplace fee on the selling price (unit %; default 15)
- Units you would sell without the deal (default 100)
- Units sold during the deal (default 260)
- Deal fee and ad spend (default 500; optional)
- Currency

## Results
- Extra profit from the deal
- ROI on deal cost
- Units needed to break even
- Deal price
- Profit per unit at deal price
- Profit without the deal
- Profit with the deal
- Deal cost (discount given + spend)

## Formula

```
Unit profit = Price × (1 − Fee%) − Cost;  Extra profit = Deal units × Deal unit profit − Spend − Baseline units × Regular unit profit;  ROI = Extra profit ÷ (Spend + Deal units × Discount per unit)
```

Where:
- Baseline units: what you would have sold at full price in the same period
- Spend: deal fee, coupon fees and advertising for the promotion

## Worked example
1. Regular unit profit = 40 × 0.85 − 18 = 16, so 100 units = 1,600.
2. Deal price 32; unit profit = 32 × 0.85 − 18 = 9.20; 260 × 9.20 − 500 = 1,892.
3. Extra profit = 1,892 − 1,600 = 292; deal cost = 500 + 260 × 8 = 2,580; ROI = 11.32%.
4. Break-even = (1,600 + 500) ÷ 9.20 = 228.3, so 229 units.

**Result:** The deal earned 292 more than selling at full price, an 11.3% return on its cost; it needed 229 units to break even.

## What the result means

Extra profit is the number that matters; revenue and units always look good during a deal. Any later lift from better ranking or reviews is a bonus not counted here, and any sales pulled forward from next month are a cost not counted here.

## Assumptions and limits
- The marketplace fee is a percentage of the selling price.
- Unit cost is the same with and without the deal.
- Halo effects on other products, post-deal ranking changes and pulled-forward demand are not modelled.

## Questions

### How do I estimate baseline units?

Use sales of the same product in a comparable period without a promotion, adjusted for seasonality.

### Why is ROI low even though sales tripled?

Because each discounted unit earns much less, and you also gave the discount to customers who would have bought anyway.

## Related calculators
- [ROAS Calculator](https://calculators.geekmidst.com/calculators/roas-calculator)
- [ROI Calculator](https://calculators.geekmidst.com/calculators/roi-calculator)
- [Discount Calculator](https://calculators.geekmidst.com/calculators/discount-calculator)
- [Break-even Calculator](https://calculators.geekmidst.com/calculators/break-even-calculator)

Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/marketplace-promotion-roi-calculator