How to read an MOT history before buying a used car
The MOT history is the only part of a used car's past that the seller cannot edit. Every test since 2005 is on record with the date, the mileage the tester read off the dashboard and every defect and advisory they noted. It takes a minute to read and it is free, so it is the first thing to do with any advert, before you arrange to see the car.
Enter the registration in the MOT check and work through the report in this order.
1. Mileage that goes backwards
The report plots every mileage reading. If any reading is lower than the one before, the report flags it. Usually it is a tester's typo, which is harmless. Sometimes it is a replaced instrument cluster, which should come with paperwork. Occasionally it is a clocked car, and the MOT record is how clocked cars get caught, because the seller cannot remove the old reading. Ask the seller to explain any backwards step before you travel.
2. Mileage that is far above or below normal
The report says how many miles a year the car averages and, where there is data, what is typical for the model. A car doing 25,000 miles a year has been a commuter or a taxi and will be worn accordingly, however clean it looks. A car doing 2,000 miles a year has sat still, which is bad for brakes, tyres and batteries in its own way.
3. Advisories that repeat
An advisory is an item the tester noticed wearing but which passed on the day. One advisory is normal; the same advisory on two consecutive tests means the owner ignored it for a year, and that tells you how the car has been looked after. The report pulls the most recent advisories into their own panel and attaches a risk figure to each, because we followed millions of cars from one test to the next: an advisory on lights becomes a failure 36% of the time, on suspension 22%, on tyres 5%.
4. Corrosion
On a car over ten years old, a corrosion advisory is the one to take seriously. Rust in a structural area only gets worse, and once a car starts failing on it each year costs more than the last. Lights and tyres are cheap to put right; sills and subframes are not.
5. Fails, and how quickly they were fixed
A fail followed by a pass a day or two later is the normal pattern: the garage fixed what it found. A fail followed by a long gap is a car that sat off the road, possibly SORNed, possibly waiting for an owner who could not afford the repair. Either way, ask.
6. How it compares with its model
At the bottom of the report the car is set against every other example of the same model and year in the DVSA dataset: the pass rate, the first-MOT pass rate and the defects that most often fail it. A ten-year-old car of any make fails about three times in ten, so compare like with like. The full reliability page for the model lists the failure rate for every year and mileage band, which tells you what the next few years are likely to cost.
What the history cannot tell you
It does not show accident damage unless the tester noted it, it does not show finance or theft, and it says nothing about service history. For those, the V5C, a receipts folder and a proper inspection still matter. But a clean MOT history with sensible mileage, no repeated advisories and no corrosion notes rules out most of the cars you should not buy, and it costs nothing to check.