Seller guides and calculators

Each page below explains one money question for an online seller and has a calculator where there is a sum to do.

All are our own writing. They give the method and made-up examples, and they leave fee tables and tax rates to the official pages, because those change.

• Seller fees explainedEvery kind of charge to count
• Pricing checklistTwelve questions before you list
• Margin vs markupConvert and compare
• GST inclusive priceAdd and remove GST correctly
• ReturnsWhat a return rate costs
• Ad spendROAS, ACOS and break-even
• DiscountsExtra sales needed
• BundlesSell two with a saving
• Cash flowMoney tied up in stock
• Break-evenUnits to cover fixed costs
• Target pricePrice from a margin

Keep going

• Profit calculatorStart here
• By productEight examples

Fee percentages, GST rates and other figures in the examples on this site are made up to show the working. They are not the fees or rates of any marketplace or country: type the numbers from your own seller account and from the tax authority. Checked 14 November 2026.