What this calculator assumes
Margin means contribution divided by item revenue plus customer shipping. The percentage fee is applied to that same revenue base. The initial 15% fee is an editable example—not an Amazon or Walmart rate lookup. Enter the actual applicable costs and test alternative assumptions.
Product cost is per sellable unit, not per carton. Include a cost only once. When your product-cost input already includes shipping or fulfillment, do not add it again in another field. Taxes, tiered fees, promotions, refunds and currency conversion are not automatically modeled. Add a justified per-unit allowance to other costs where appropriate, and verify the fee base against your marketplace records.
The minimum-price formula
Item floor = total per-unit cost ÷ (1 − fee rate − target margin) − customer shipping. The result is rounded upward to the next cent and never below zero. When fee plus margin reaches 100%, this model has no valid denominator.
For the starting example, total cost is $16 and fee plus target margin is 30%. The item-price floor is $16 ÷ 0.70 = $22.857…, rounded upward to $22.86. A 0% margin target remains a valid break-even scenario; the tool does not change any account’s target.
Why a small price cut can need a large sales increase
At a $25 item price, the example contribution is $25 × 0.85 − $16 = $5.25 per unit. At $24 it becomes $4.40. Maintaining the same total contribution would require about 19.3% more units, assuming every other input stays unchanged. That is a break-even requirement, not evidence that demand will increase.
The comparison uses old contribution ÷ new contribution − 1. When the proposed contribution is zero or negative, additional sales cannot restore the old positive contribution under these assumptions. When the baseline itself is not profitable, review costs and prices before using this ratio.
Use the result alongside evidence
Check the actual listing price and its timestamp, the relevant competing offers, your chosen limits and the observed marketplace response. A calculated floor alone does not prove Buy Box eligibility, consumer demand or final profit.