How to Calculate True Profit on a Used Car

Gross margin is the simplest number to calculate, which is exactly why it's the one most dealers end up tracking: sale price minus purchase price. It's a useful headline figure, but it's not what actually landed in the bank once every real cost of that vehicle is accounted for.

True profit (sometimes called net profit per unit) takes gross margin and subtracts everything else that was genuinely spent getting that specific car ready and sold: preparation work, transport, any stocking finance interest accrued while it sat unsold, and selling costs like portal advertising fees or a warranty provided to the buyer. It's more work to track, but it's the number that actually tells you whether a vehicle — or a whole sourcing channel, or a whole model line — was worth buying.

Say you buy a car for £6,000. You spend £450 on an MOT, service and valet, £80 on collection, and £120 on advertising and a 3-month warranty for the buyer. You sell it for £8,200.

The naive calculation: £8,200 − £6,000 = £2,200 "profit".

The true profit calculation: £8,200 − (£6,000 + £450 + £80 + £120) = £8,200 − £6,650 = £1,550.

That's a £650 gap between what looks like the profit and what actually is — on one car. Run that same gap across 100 cars a year and it's £65,000 of margin a dealer might believe they have but don't, which matters a great deal when deciding how much to reinvest in stock or draw out of the business.

Lumping prep costs into one general "workshop" or "overheads" bucket instead of recording them against the specific vehicle they were spent on — this makes it impossible to see which vehicles, sources or models are actually the most profitable to buy again.

Ignoring the cost of capital: money tied up in a vehicle that sits unsold for 90 days has a real cost, whether that's stocking-loan interest or simply the opportunity cost of not having that cash available to buy the next car.

Forgetting buyer-facing costs — a warranty, a tank of fuel, a courtesy repair — that come out of the deal after the sale price is agreed.

Reviewing only monthly or aggregate profit totals, rather than per-vehicle true profit, which hides which individual deals or vehicle types are quietly dragging the average down.

Record purchase price and every cost as it's actually incurred — at the point you pay for prep work or transport, not reconstructed from memory at month-end.

Review true profit per vehicle, not just the monthly total, so you can see which sources and models are genuinely worth repeating.

Track margin percentage alongside the absolute profit figure — a car that made £500 quickly can outperform one that made £900 slowly, once stock-turn is taken into account (see our guide on stock turn below).