Free tools for people who buy to resell

The calculators do their math in your browser, and nothing you type into one is sent to us. No sign-in.

• Amazon Q4 fee calculator

  Estimate profit per unit with the referral fee and the 2026 holiday peak surcharges.

• Resale profit and ROI calculator

  Profit, return on cost and break-even price for a resale, with the marketplace fee you enter.

• Maximum buy price calculator

  The most you can pay for an item and still hit your profit or return-on-cost target.

• UPC and EAN check digit checker

  Check that a barcode number is typed correctly, or work out a missing check digit.