01 Revenue is a weak operating signal
Two stores can report the same revenue and have completely different businesses. One may generate cash from every order. The other may be buying growth through discounts, expensive traffic, shipping subsidies, and returns.
Contribution margin strips away the vanity. It shows what remains after the variable costs required to create and fulfil a sale.
02 The calculation founders need
Start with net sales. Subtract product cost, freight and duties, fulfilment, payment fees, marketplace commissions, discounts, returns, and variable acquisition cost. What remains must fund payroll, software, rent, tax, and profit.
Net sales − variable product, fulfilment, channel, and acquisition costs = contribution margin.
03 One blended margin hides the problem
Calculate contribution by product, market, channel, and customer cohort. A profitable DTC channel can hide a marketplace leak. A strong hero product can subsidise a catalogue that should be simplified. A high first-order CAC may be rational for a cohort with proven repeat behaviour, but dangerous when retention is assumed.
- Use actual return rates, not a company average.
- Assign fulfilment and payment costs to the channel that creates them.
- Separate first-order economics from repeat-order economics.
04 Turn margin into decisions
Once the number is trusted, it becomes the operating language of the business. It sets the maximum CAC, shows which promotions are affordable, informs stock bets, and reveals whether revenue targets improve or weaken the company.
The goal is not the highest possible margin on every order. It is knowing exactly where margin is created, where it is deliberately invested, and where it is disappearing without a return.