When you read a PlateInsight guide, every vehicle is ranked by a reliability score and accompanied by pass rates, defect data, and sample sizes. This page explains where those numbers come from, how they are calculated, and what they mean.
The Data
Every score and statistic on this site comes from the complete archive of MOT test results published by the UK’s Driver and Vehicle Standards Agency (DVSA). This is the official record of every MOT test conducted at every testing station in the country. Not a sample, not a survey, not an opinion poll.
We have processed and analysed over 261 million individual MOT test records covering more than 18.9 million unique vehicles.
Every vehicle over three years old in the UK must have an annual MOT. So we are not relying on voluntary owner surveys or manufacturer claims. We are looking at what actually happens to real vehicles, on real roads, inspected by independent testers. A car that looks good on paper but racks up brake defects from 50,000 miles cannot hide from this data.
Each MOT record includes the date of test, the result (pass or fail), the vehicle’s recorded mileage, and a full list of any defects found. Defects are categorised by type, location, and severity (advisory, minor, major, or dangerous). We process this raw data into structured profiles for every make, model, year, and fuel type combination on UK roads.
What the Reliability Score Means
Each vehicle configuration in our rankings is assigned a reliability score. This score answers a simple question: how does this vehicle compare to others like it?
The score is calculated by comparing the vehicle’s MOT pass rate against a benchmark — the expected performance for vehicles of the same age, fuel type, and mileage range. A vehicle that consistently passes its MOT at a higher rate than its benchmark scores higher. One that underperforms scores lower.
This benchmark-relative approach matters because it creates a fair comparison. A 10-year-old car will naturally have a lower raw pass rate than a 4-year-old car, but that does not mean it is less reliable for its age. Our scoring adjusts for this, so you can meaningfully compare vehicles across different ages and types.
Higher scores are better. When browsing our Vehicle Explorer or reading our guides, use the score as a quick way to identify which vehicles have the strongest track record in real-world MOT testing.
Pass Rate
Alongside the reliability score, each vehicle shows a pass rate, the percentage of MOT tests that vehicles of that type pass. It is the simplest measure of reliability: how often does this car pass its annual inspection?
Pass rates above 88% are strong. Between 80% and 88% is typical for well-maintained models. Below 80% suggests the model has a higher-than-average incidence of MOT-relevant issues.
Keep in mind that pass rate alone does not tell the full story. Two vehicles might both pass at 85%, but one accumulates three advisories every year while the other passes clean. That is why we use the broader reliability score as the primary ranking metric, with pass rate as a supporting data point.
Defect Data
Where available, our vehicle cards show the most common defects found during MOT testing for that model. These are the specific issues (worn brake pads, corroded suspension components, lighting faults) that testers flag most frequently.
Each defect is shown with its occurrence rate (how often it appears across tests) and its severity level:
Advisory
A potential future issue that does not currently affect roadworthiness. The vehicle still passes, but the tester is flagging something to monitor. A brake pad wearing thin but not yet at the legal minimum is a typical example.
Minor
A defect that does not cause a test failure but represents a problem that should be repaired. The vehicle passes, but the issue is recorded and the owner is advised to address it.
Major
A significant defect that causes an MOT failure. The vehicle cannot legally be driven until the issue is repaired and the car is retested. Heavily worn brake discs, structural corrosion, and emissions failures all fall into this category.
Dangerous
A defect that poses a direct and immediate risk to road safety. The vehicle fails and should not be driven at all until repaired. These are rare but serious, think fractured steering components or severely corroded brake lines.
Knowing which defects are common for a particular model helps you understand what to look for during a viewing, what questions to ask a seller, and what maintenance costs to budget for.
Sample Sizes
Every vehicle card shows the number of tests and number of vehicles behind the score. This transparency matters because a score based on 50 vehicles is less reliable than one based on 50,000.
Popular models like the Ford Fiesta, Vauxhall Corsa, and Volkswagen Golf have hundreds of thousands of test records behind their scores. Rarer vehicles with smaller samples are included where the data is sufficient, but you should weigh the scores accordingly. A high score from 200 tests is less certain than the same score from 20,000.
Mileage Data
Where shown, typical mileage and annual mileage figures are derived from the odometer readings recorded at each MOT test. Because every vehicle is tested annually, we can track mileage accumulation over time and calculate medians for each vehicle type.
This is useful context when evaluating a specific car. If the typical mileage for a 2017 Ford Focus is 62,000 miles, and the one you are considering has 90,000, that does not automatically make it a bad buy. It does mean it has been driven harder than most of its peers, though, and its wear items may be further along.
What the Data Does Not Tell You
We believe in being transparent about what our data can and cannot do.
MOT data captures defects found during an annual inspection. It does not capture problems that occur between tests, repairs carried out by owners proactively, or issues with components outside the MOT test (air conditioning, infotainment systems, interior trim). A vehicle with a high reliability score may still have non-MOT issues that affect the ownership experience.
Our scores reflect the general pattern for a vehicle type. Individual cars within any model can vary significantly depending on how they have been driven, maintained, and cared for. We always recommend a physical inspection alongside any data check.
How We Keep the Data Current
Our database is updated regularly as new MOT test records are published by the DVSA. Scores and rankings evolve over time as new data becomes available. A model that performed well five years ago may show emerging issues in more recent test data, and our scores will reflect that.