Why it matters
A store can report strong revenue while losing money if advertising consumes the contribution available after product, fulfillment and marketplace costs.
Break-even ROAS ≈ Revenue ÷ Maximum Affordable Ad Cost
Do not scale at the boundary
A business normally needs a safety margin above break-even to absorb refunds, volatility, overhead and measurement error. The correct target depends on your economics and business objectives.
Use the numbers
Educational guidance is most useful when paired with your own SKU economics. Run the same assumptions through the calculator, then compare marketplaces if channel selection is part of the decision.