Calculator
Unit Economics Calculator
What's left after the platform takes its cut? Work out true profit per unit on Amazon, Shopify, eBay or Etsy — including ad spend, returns, and payment processing.
Platform
Price & cost
What it costs you to acquire or manufacture the product.
Box, label, postage. For FBA this is included in the platform fee — set to £0.
Fees & ads
Amazon referral fee — typically 8–15% depending on category.
Amazon FBA fulfilment fee for a small/light item. Larger items cost more.
Set 2.9% for Stripe / Shopify Payments. Amazon and eBay typically include this in the platform fee — leave at 0.
Average cost to acquire one sale (PPC, social ads, influencer).
Industry average is 5–15% depending on category (apparel highest).
Used to project monthly contribution profit.
Calculations happen entirely in your browser. Nothing is saved or sent anywhere.
Where each £29.99 goes
Contribution margin is profit per unit before ad spend — what each sale contributes to covering fixed costs and ad budgets. Max ad spend is the most you can pay for a customer before the unit becomes unprofitable.
How unit economics works
Unit economics asks one question: how much money do you actually keep when you sell one unit? Headline revenue is meaningless if marketplace fees, shipping, returns and ad spend swallow it on the way to your bank account. This calculator strips revenue down to contribution margin per unit — the number that decides whether your business scales profitably or just expensively.
The formula
Contribution per unit = Selling price − COGS − Platform fee − Payment fee − Shipping − Packaging − Ad cost per unit − Returns provision
Multiply contribution per unit by units sold to get total contribution; that's the pool that pays for fixed costs (rent, salaries, software) and, eventually, profit.
Worked example
Scenario: Selling a £30 product on Amazon UK with FBA. COGS £8, FBA fee £4, referral fee 15% = £4.50, shipping inbound £1, packaging £0.50, £2 of ad spend per unit, 5% return rate = £1.50 provision.
Total per-unit costs: £8 + £4 + £4.50 + £1 + £0.50 + £2 + £1.50 = £21.50
Contribution per unit: £30 − £21.50 = £8.50 (28% margin)
At 200 units/month: £1,700 of contribution — which has to cover all fixed costs before anything is profit. Bumping price by £3 takes margin to 38% — a much healthier business.
Frequently asked questions
What is unit economics?
Unit economics is the profit (or loss) on a single unit sold. It's the foundation of any e-commerce business: if a unit isn't profitable in isolation, no amount of volume will fix it. The number to focus on is contribution margin — selling price minus all variable per-unit costs.
What costs should I include?
Cost of goods sold (the product itself), platform/marketplace fees, payment processing fees, fulfilment and shipping, packaging, ad spend allocated per unit, expected returns/refunds, and any per-unit handling fees. Fixed costs (rent, salaries) are excluded — those are covered by total contribution, not per-unit profit.
How do platform fees compare?
Roughly: Amazon charges around 15% referral plus FBA fees that vary by size; eBay around 13% final value plus payment fees; Etsy 6.5% plus payment processing; Shopify charges no marketplace fee but you pay payment processing (~2.9% + 30¢ for Shopify Payments) and your own ad costs.
Should I price for break-even or for margin?
Always price for margin. Once contribution per unit is positive and meaningful (typically 30%+ for physical goods), volume becomes profitable. Pricing at break-even or below to win volume is a trap — competitors with deeper pockets will simply outlast you.
How does ad spend per unit work?
Total ad spend ÷ units sold = ad cost per unit. If you spend £2,000 in a month and sell 100 units, that's £20 per unit deducted from contribution. Improving conversion rate or reducing CPC drops this number directly. See our ROAS calculator for the campaign-level view.
What about returns?
Returns are a hidden killer. A 10% return rate on a £30 product means every sale needs to absorb £3 of expected refund cost (or more if you also lose the goods). Apparel and beauty often run 20-30% return rates; consumables run under 2%.