How this calculator helps
Reseller margin should reflect what actually leaves your account: platform fees and postage are common first-order adjustments.
Formulaprofit = sell − cost − ship − sell×(fee%/100), margin% = (profit÷sell)×100
Model note
Fees are modeled as a percent of the selling price. If your platform mixes percent and fixed fees, approximate with an effective percent or fold fixed fees into shipping/cost lines.