Accuracy Transparency

One of the questions we get asked most by customers is; ‘How do you set your valuations?’

There's a perception that it's some kind of ‘dark art’, but it's all based on real world observations, market feedback and years of experience. Plus a little caffeine.

Here we explain just what goes into producing our car valuations and the processes we go through.

Every month we will publish our latest accuracy figures here regardless of the outcome. We promise to be completely transparent on exactly how accurate we were.

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Want to know more about our data?

Fill in the form below to learn more about our data or trial our valuation solutions. Or you can call the team on 0203 897 2500.

What we put into our valuations every year

We receive car auction sale observations from The National Association of Motor Auctions (NAMA) every month and retail observations from a variety of web portals such as motors.co.uk and AA Cars.

Our team of Car Editors meet with customers, motor trade experts, manufacturers, dealers and auctioneers as well as car rental companies and leasing and contract hire customers.

We've also got history, more than 80 years of it in fact, and all the learnings and experience passed n through the generations go into our valuations. Our current Editorial team on their own have over 200 years' experience in the automotive industry. They might not all qualify as ‘classics', but they certainly know their stuff.

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Our valuation process

Our valuation process is vital, and our monthly Editorial meeting is the focal point of the process. It's a forum where the team discusses everything they've seen in the market, feedback from customers, auction houses, dealers, fleet managers and more.

An agreed valuation policy is agreed and applied to the data as a whole, usually in the form of what the average depreciation percentage should be. We also highlight strong performing sectors, manufacturers or models that are exceptions to the rule and adjust them accordingly.

Every market sector is considered with the same care and attention. This means values from the initial forecasts of pre-production models through to the used values of the oldest cars have been considered by our highly experienced team.

Glass's uses a valuation tool developed over many years that utilises a primary/secondary model structure. This is the absolute start point of the valuation process, having the right curve in place to detail the correct rate of depreciation. We overlay the previous months' market activity, high quality econometric factors and short term market sentiment, to create a comprehensive set of reliable, justifiable and high quality market information.

At every point, our Editors will manually make changes to the data and values when necessary. Our Editors also review and correct any anomalies in the data ‘by hand' before the final values are set. Each month, we accurate value over 50,000 models. You can see how accurate we've been each month in the interactive chart below.

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Accuracy reporting archive.

Accuracy matters

Giving you the full picture

We will always compare ourselves to the market on EVERY vehicle we can. This usually means 60,000 to 80,000 a month.

We will never cherry pick a small section of observations to make us look more favourable; we'd be lying to ourselves and more importantly, you. We have customers specialising in every area of the market so we need to be just as accurate on late plate, low mileage cars as we are on ten year old, high mileage vehicles. Accuracy matters to us, but it matters more to you.

How do we measure accuracy?

  1. Trade observations are received from NAMA and matched to the relevant Glass Code
  2. Our standard mileage Glass Trade figure is identified from the same month as the observation
  3. The Glass Trade figure is adjusted to the exact mileage figure of the observation
  4. Auction hammer price is compared to the mileage adjusted Glass Trade value
  5. We then look at the average overall accuracy figure, which is the trade value against the observed auction price – the closer to 0%, the more accurate we are.

Why are we not more accurate?


Our variance in accuracy is affected by 'surprise' market movements that cannot be foreseen when producing the data. These can range from a period of exceptionally good weather that keeps buyers away from the forecourt, to a leasing or contract hire company dropping a large number of the same car into the market unexpectedly, impacting desirability, availability and therefore values. In the case of low volume models such as prestige cars, two or three extra cars in the market can make all the difference.


It should always be remembered that our 'static' Trade valuations are a guide only and are a UK wide valuation, so there will be regional variations that are not considered in this data set (we have a product called Radar that offers region specific Live Retail Pricing).

Want to know more about our data?

Fill in the form below to learn more about our data or trial our valuation solutions. Or you can call the team on 0203 897 2500.

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