How Does Part-Exchange Actually Work in the UK?

The one number that matters

Part-exchange (PX) is the deal where the dealer takes your current car as partial payment for the next one. It feels like one transaction; it's actually two. You're selling a car AND buying a car. The dealer wants the price-of-sale-minus-PX-value (the 'cost to change') to look low, because that's the number you remember walking off the forecourt with.

Negotiate the cost to change last. Negotiate the new-car price first, in cash terms, ignoring your part-ex entirely. Then introduce the part-ex and watch the dealer's behaviour: a dealer who suddenly bumps the new-car price 'because we can give you more for your trade-in' is moving margin around, not adding value.

How they calculate the PX figure

Trade dealers value cars against the CAP Black Book — the industry's auction-baseline guide, updated monthly. They take CAP Clean (what a tidy example is worth), then subtract: a) reconditioning estimate (paint, valet, MOT, mechanical fixes), b) margin (typically £500–£1,500 for sub-£10k cars, £1,500–£3,000 above), and c) risk allowance for unknowns.

So if your car is CAP Clean £8,500, expect a PX offer of £6,000–£6,800. Anything above that, the dealer is taking your car as a loss-leader to win the bigger deal. Anything well below that, they're banking on you not checking.

Mileage hurts more than age past a certain point. A car with 85,000 miles takes a £500–£1,000 hit vs the same car at 65,000. Service history hurts even more — no service history can knock 10–15% off the offer. Tidy paint, four matching tyres, a fresh MOT — each adds £100–£300 in the dealer's recon estimate, which they pass back to you as a higher offer.

PX vs private sale — when each wins

Private sale almost always pays more — typically 10–25% more than PX, because you're capturing the dealer's margin yourself. On a £6,000 car that's £600–£1,500 in your pocket.

But private sales cost time. Photos, listing fees, time-wasters, test drives with strangers, payment risk, and the gap between 'sold mine' and 'bought next'. If your car is straightforward (under £10k, popular model, clean history) the private sale is worth the effort. If it's awkward (high mileage, niche model, needs work) you may struggle to beat the PX figure once you discount for the time spent.

WeBuyAnyCar and similar services sit in the middle. Convenient, instant cash, but their offer is typically 15–25% below CAP Clean — i.e. similar to or slightly worse than a forecourt PX offer. Use them for a price check, not as your default exit.

If you're trading down (selling expensive, buying cheaper), you may walk out with cash from the dealer in your bank — they pay you the difference. If you're trading up, the PX figure simply reduces what you owe.

Getting the best PX offer

Wash and vacuum the car the day before — yes, really. A dealer who has to discount for valeting WILL discount for valeting. £20 of effort = £100–£200 on the offer.

Take three CAP figures (free at carpricecheck.com or similar) with you. CAP Average / Clean / Below show the spread for your year, mileage, and condition. Use the Average figure as your floor; anything below that is a low-ball.

Get more than one PX quote. Three dealers, same week, same car. The spread is usually £500–£1,500 — easy money for an afternoon's driving. Tell each dealer the others' offers (it's expected — they assume you have).

Time it right. Dealers chase quarter-end (March, June, September, December) and year-end registration plates (March, September). PX offers are typically 5–10% better in the last two weeks of those months because the manager needs the trade-in to make a deal close.

Watch-outs in the paperwork

The PX offer is conditional until the dealer inspects the car. If you're collecting your new car in two weeks, the offer can be revised down on hand-over day if anything's changed. Don't take the new car if the PX figure has moved without your agreement.

Outstanding finance on your trade-in must be settled by the dealer (or you, before the deal closes). The dealer typically handles this — they request a settlement figure from your lender, pay it directly, and the difference goes against your new-car price. Get it in writing, including the settlement figure.

V5C and a spare key on the day. Missing key = £200–£400 deduction. Missing V5C = the deal usually still closes but your PX figure can be revised.