How many units before you stop losing money

Fixed costs are what you pay whether or not you sell anything. Variable cost is what each additional unit costs you. The gap between price and variable cost is what pays down the fixed side.

How this is calculated

Fixed costs divided by contribution per unit, rounded up to a whole unit. If contribution is zero or negative the result is meaningless — no volume rescues a product that loses money on every sale.

Questions

What counts as a fixed cost?
Rent, subscriptions, your own salary, accounting fees — anything that arrives whether or not an order comes in. Marketplace commission is variable, because it only exists when you sell.
Should I include returns?
Fold your return rate into the variable cost per unit. If one in twenty orders comes back and costs you shipping both ways, that expected cost belongs on every unit you sell.

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