The Maths of a Flip

Take a GameBoy Advance SP from a bric-a-brac stall. Six pounds paid. It sells on eBay four days later for 62. Most people call that 56 pounds of profit. It is not.

Landed cost first: the six pounds, plus the two you spent on a spare charger to test it, plus nothing for cleaning. Eight pounds in. Then the sale: eBay's final value fee at around 12.8 percent plus thirty pence comes off the 62, and postage out comes off if the buyer did not pay it. Call the net 52. Profit is 44, and ROI, profit over landed cost, is about 550 percent. Still a brilliant flip. Just not the number you told your mate.

Each platform in Flipfox carries an editable fee estimate. eBay and Etsy have percentage plus fixed components; Vinted and Depop default to zero because the buyer pays. When a sale comes in through the official eBay connection the estimate is replaced with the actual fees from eBay's own finances data, so the number on your Home screen is what landed in your account, not a guess.

Den Check scores your stock's health out of a hundred and explains the score. Unlisted items earn nothing, so they cost points. Stale stock, held 45 days or more, costs points. Items with no target price cost points, because you cannot measure a flip you never priced. The score is on Home, and the fixes become quests.

When something has sat too long the Rescue queue suggests a markdown: fifteen percent off at 45 days, thirty at 60, and never below the floor price you set when you bought it. Flip is asleep in the header of that screen, which is the joke: this is the cash that has been napping.

Intel does the longer view. Best brands, best sources, best categories, sell-through, and capital velocity, which is how fast money goes out and comes back, filtered by period. It is the screen that tells you to stop buying dresses and go back to the bric-a-brac.

The tax view produces a planning estimate for a UK sole trader on the cash basis for the 2026/27 year: income tax plus Class 4 National Insurance on profit after expenses, mileage and working-from-home allowances, and a check against the trading allowance for anyone under the threshold. It suggests a tax pot to set aside and exports to CSV. It is a planning tool with a disclaimer on it, not an accountant, and personal clear-out sales never enter it.