What these tools are for
Our three calculators help compare the contribution of a bundle, the contribution of a bulk discount and the operating cost of expected returns. The public project identity is SellerMargin Tools. The examples are illustrative and are not results from a named store or a claim about marketplace performance.
How we define the outputs
Order contribution is selling revenue minus the item costs, percentage charges and fulfillment expenses entered in the form. Margin divides that contribution by selling revenue. Return cost combines additional processing expenses with an expected inventory write-off. Definitions and full formulas appear next to each tool so you can compare them with your own records.
How calculations are checked
The calculation engine is shared by all three tool pages. Its regression suite contains 299 checks: worked examples, fee treatment, equal-quantity comparisons, zero values, break-even boundaries and rejection of invalid inputs. Browser checks also exercise input changes, reset actions, navigation and responsive layouts. These checks reduce implementation errors; they do not validate every business assumption for your store.
Calculations retain their internal numeric precision until display. Monetary results are shown in US dollars to the nearest cent. Values displayed in separate rows can therefore differ slightly from arithmetic using only the rounded rows. A displayed break-even price is rounded for readability; round up if you need a cent-denominated price that meets the threshold.
Editorial and correction approach
The guides explain the specific arithmetic used by the working forms. We avoid presenting assumed conversion improvements, current fee quotes or industry averages as facts. When a formula or example changes, its regression expectations must be reviewed together. An input that is invalid removes the old result rather than leaving a stale estimate visible.
Independence and limitations
SellerMargin Tools is not affiliated with Google, Cloudflare or a marketplace. No platform account is connected to the calculators, and no professional accounting, legal or tax review is represented. Use your own records to check the entered fee base, shipping assumptions and cost allocation before relying on a pricing decision.
Data and funding
There is currently no registration, advertising code or analytics code on the site. The calculators do not store or transmit entered numbers. Standard hosting requests are handled by Cloudflare; see the privacy policy for details.
Methodology reviewed October 27, 2026.