MOT pass rate is the most-quoted figure in UK car reliability writing, and the least-understood. Before you use a pass rate to decide anything — whether to keep your car, buy a used one, or pick a garage — it helps to understand what the number is actually counting.
What a “pass rate” is
A first-time MOT pass rate for a given make and model is calculated as:
(tests marked P — Pass) ÷ (all test outcomes logged for that make and model)
The national MOT record logs three outcomes we care about:
- P — the car passed first time.
- PRS — it passed after rectification at the station. Something was fixed during the test window.
- F — it failed outright.
Every per-car pass rate on MOTCost uses the first definition. We quote PRS separately because blending it into “pass” hides a real mechanical event: something on your car didn’t meet standard when it arrived at the centre.
What a pass rate isn’t
A high pass rate does not mean a car is reliable. A car that passes its MOT is, at minimum, road-legal — the MOT is a safety test, not a “this car won’t break down” certificate. Brakes, tyres, lights, steering, suspension, emissions: if those work, the MOT passes. Ignore intermittent electrical faults, slow cooling-system leaks, or gearbox whine and your car can still tick the pass box on the day.
A low pass rate also doesn’t necessarily mean the model is bad. Older cars fail more. A model that ages in the fleet — owned for ten years, driven hard by second and third owners — will have a worse MOT record than a newer model whose average owner sells it at four years. The first-use date range on each car page hints at this; we quote it so you can read the pass rate in context.
Where the data comes from
Every figure on MOTCost is drawn from the Department for Transport’s published MOT test record, released annually under the Open Government Licence. The dataset covers tens of millions of individual test events for each annual vintage, plus a separate defect record that lists every Reason for Rejection logged at test. Both are publicly downloadable.
Why per-model rates bounce around
A single Ford Fiesta passing or failing its test doesn’t move the national average — the Fiesta line has 1.7 million tests behind it. A Lotus Evora, however, might log a few thousand. A model with a thin sample size will produce a volatile pass-rate number. We apply no statistical smoothing. The figure is the raw ratio of passes to total tests in that year.
For cars with fewer than 500 tests we’d recommend treating the pass rate as indicative, not definitive. If you care about the exact reliability of an obscure model, the pass rate on MOTCost is the starting point for a conversation, not the answer.
What a failure list really tells you
Every car page ends with a ranked list of the ten Reasons for Rejection — the codes a tester logs when a Major or Dangerous defect is found. These lists are the most useful piece of data on each page. They tell you, drawn directly from the national test record, what a tester is most likely to flag on a car like yours.
Use the list as a pre-MOT checklist. If the top three failures for your model are tyre tread depth, stop-lamp bulbs, and worn brake pads, it’s worth a twenty-minute walkaround before booking the test. If they’re suspension bushes and wheel bearings, budget accordingly.
The list does not tell you that every car of that model has those faults. It tells you that, across the fleet, those are the things testers are pulling up most often. That’s a different claim, and the more honest one.