Fixed cost basis
Purchase + repairs + cleaning + shipping + taxes paid + storage + advertising + other costs.
Total cost
Fixed cost basis + expected sale price × combined fee rate. This includes expected selling fees.
Break even
Fixed cost basis ÷ (1 − combined fee rate). The combined fee rate must be less than 100%.
Gross and net profit
Gross profit here means sale price less purchase price. Net profit subtracts all entered costs and fees. These are planning definitions, not formal accounting statements.
Margin and ROI
Margin = net profit ÷ sale price × 100. ROI = net profit ÷ fixed cost basis × 100. A zero denominator is reported as not defined.
What is excluded?
Unentered costs, income tax, financing, refunds and changing demand are not modeled. Marketplace fee bases can differ; verify actual fee rules and adapt your inputs.