Useful math for small shops.

Margin Lab helps independent sellers see what remains after the cost of fulfilling an order. The calculator is free, uses transparent formulas and keeps your calculations in your browser.

How the calculation works

Break-even price divides fixed per-item costs by one minus the percentage fee rate. Target price additionally subtracts the target margin from that denominator. A target is not achievable if the remaining denominator is zero or negative.

Assumptions and limitations

All inputs use USD. Percentage fees apply only to the item price. Add any fee charged on shipping or taxes to fixed fees. The tool does not include overhead, income taxes, returns or discounts unless you account for them in your inputs. It does not promise business profitability.

How this project may earn money

The planned business model is optional paid digital templates. The calculator and guides remain free. There are currently no paid endorsements, affiliate commissions or live paid checkout on this site.

Editorial approach

The guides use original, illustrative examples prepared with AI assistance. They explain the math rather than claim specific marketplace fees or guaranteed outcomes.