How the MOT reliability score works
The reliability score compares how often a model fails its MOT with how often the average car of the same age and mileage fails. 100 is average; a higher score means fewer failures than expected. It's built from all 30,771,766 first MOT tests of cars aged 3 to 20 that DVSA recorded in 2024. Updated 2026-09-29.
Definitions
- MOT test: a class 4 test (cars and small vans) recorded by DVSA in 2024. Only the first test of each MOT counts, not retests.
- Fail: the car failed, or had a defect fixed during the test (“PRS”, pass after rectification), which is DVSA's own definition of a first-time failure.
- First-time fail rate: fails divided by first tests. Across all cars aged 3 to 20 it was 28.5% in 2024.
- Ages 3 to 20: cars take their first MOT at three; older cars are rare and atypical. Taxis and private hire cars tested yearly from new are excluded by the age limit.
- Model: DVSA's make and model, grouped into model families (every Fiesta is a Ford Fiesta), so all versions and generations are combined. Comparisons of older generations use the model's tests at the ages that generation would be.
The formula
Older, higher-mileage cars fail more often, so raw fail rates flatter newer, less-used models. For each model we work out how many of its tests would have failed if it behaved like the average car in each age and mileage band, then divide by how many actually failed:
Reliability score = 100 × expected failures ÷ actual failures
So 125 means a fifth (20%) fewer failures than expected for its age and mileage, and 80 means a quarter (25%) more.
Worked example: Porsche 911
In 2024, 10.0% of Porsche 911 MOT tests were first-time fails. Cars of the same ages and mileages would have been expected to fail about 26.2% of the time. 26.2% ÷ 10.0% × 100 gives its score of 261, the best of any popular car.
Minimum numbers of tests
- A model needs at least 2,000 tests to appear in the league, and a make 5,000.
- The “most and least reliable” rankings use models with at least 20,000 tests, so a handful of unlucky cars can't top or tail the table.
- Fail rates at the first MOT need at least 300 first MOTs.
Limits
- An MOT checks safety and emissions on the day; it isn't a breakdown or repair record. Engine and gearbox faults that don't affect the test don't show.
- How cars are looked after matters. Premium and sports cars are often serviced by specialists and driven less, and vans work harder (they have their own league).
- DVSA doesn't record the generation, so model scores mix generations; cars from a changeover year can be either.
- Some DVSA model names are coding artefacts or truncated (a coachbuilder code, for example); we leave those out.
Data and reuse
Source: DVSA anonymised MOT tests and results, Open Government Licence v3.0. Our league is free to reuse with a link: download the CSV from the MOT Reliability League. See all our data sources.