Seller math guide
Shipping supplies cost guide
How to include boxes, mailers, tape, labels, and inserts in profit math.
Quick answer
Good seller math starts with the full cash picture: revenue, item cost, platform fees, payment fees, shipping, packaging, ads, returns, and time. If one of those is missing, the result can look profitable while cash quietly leaks out.
Workflow
- Start with expected sale price, not wishful list price.
- Subtract item cost and any inbound shipping or prep cost.
- Add platform fees, payment fees, ad cost, packaging, and outbound shipping.
- Stress test the number with a discount, offer, or return.
- Compare the final margin with your minimum target before buying more inventory.
Useful calculators
Common mistake
The common mistake is treating sale price as success. The better question is whether the final net profit is worth the money tied up, the time spent, and the risk of return or markdown.