Service History Value Calculator

Being straight about what this is: the headline figure is published, the shape of the model is ours. UK used-market guidance converges on a full service history being worth roughly 10–20% of a car’s value — Motorway puts it at “up to 20%”, and HPI approaches the same thing from the other side, expecting to knock at least 15% off a car without one and as much as 40% in the worst cases. None of those sources breaks the figure down further. Everything below is our own model, built to sit inside that published band.

• Segment split (our model). We spread the published band across brand segments — 8–15% mainstream, 12–18% premium, 15–22% prestige — on the reasoning that buyers of dearer cars scrutinise history harder and the repair bills a missing record implies are larger. That tiering is an editorial judgement, not something any of the sources below states.
• Age taper (our model). Also an editorial modelling assumption, not a measured curve: we hold the premium at full weight up to three years and then taper it gradually, on the reasoning that a documented history tends to matter most on newer cars.
• Price base. The percentage is applied to the midpoint of your chosen price band and rounded to the nearest £50. The top band, £20,000+, is modelled at a £30,000 midpoint.

Published sources for the underlying 10–20% band:

• Motorway — puts a full service history at “up to 20%” of value, and “often 10% to 20%”
• Carwow — restates the 20% upside and HPI's 40% downside for a missing record
• HPI (2018) — frames it as a discount instead: “at least 15%” off, up to “40% less”

It is an estimate to frame a decision, not a valuation. A specific car’s worth depends on condition, mileage, demand and the exact records — for which the MOT history and a full service record are the evidence.