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MOT Failure Rate by Vehicle Age: What to Expect

Your car's age is the single biggest predictor of whether it will pass its MOT. A 3-year-old car has roughly a 1-in-5 chance of failing; by 12 years, it is closer to 1-in-2. Here is what the data shows.

Failure Rates and Expected Costs by Age

Vehicle age	Initial failure rate	Avg repair cost (if fail)	Annual MOT budget	Common failures
3 years	~20%	£50-100	£60-80	Bulbs, wipers, tyres at tread limit
4 years	~23%	£60-150	£70-100	Bulbs, tyres, minor brake wear
5 years	~27%	£80-200	£80-120	Brake pads, tyres, emissions
6 years	~30%	£100-250	£90-140	Suspension wear, brake discs, exhaust issues
7 years	~35%	£120-300	£100-160	Suspension, emissions, steering wear
8 years	~38%	£150-350	£110-180	Suspension, exhaust, corroded brake lines
10 years	~44%	£180-450	£130-230	Multiple mechanical issues, early structural rust
12 years	~50%	£200-600	£150-300	Structural corrosion, exhaust failure, multiple systems
15 years	~55%	£250-800	£180-400	Extensive rust, catalytic converter, cumulative wear
20+ years	~45%	£200-1,000+	£150-500	Structural integrity, but often well-maintained classics

Annual MOT budget = test fee (£35-40) + (failure rate x average repair cost). Figures are indicative based on DVSA data and industry averages.

Why Do Failure Rates Increase With Age?

Rubber perishes

Suspension bushes, brake hoses, and exhaust mounts are all rubber components that deteriorate with age regardless of mileage. By 8-10 years, these parts are often close to failure.

Metal corrodes

Structural rust is the enemy of older cars. Sills, subframes, wheel arches, and brake lines all corrode over time, especially in areas that use road salt in winter.

Emissions systems degrade

Catalytic converters and diesel particulate filters (DPFs) lose efficiency with age. A 10-year-old car may struggle to pass emissions even if it runs well otherwise.

Wear compounds

Steering racks develop play, wheel bearings wear, and brake systems need more frequent attention. Each year adds more potential failure points.

What Typically Fails at Each Stage

Young cars (3-5 years)

First-MOT failures are usually minor and cheap. Blown headlight bulbs are the single most common issue. Original tyres reaching the tread limit is next. Wiper blades that have hardened over three summers. These are all easy, low-cost fixes that a 10-minute pre-MOT check would catch.

Mid-age cars (6-10 years)

This is where mechanical wear starts to bite. Brake pads and discs need replacing. Suspension components (shock absorbers, springs, anti-roll bar links) begin to fail. Emissions become borderline as the catalytic converter ages. Repair bills are moderate but you may face two or three issues at once.

Older cars (11-15 years)

Structural corrosion becomes a real concern, especially on cars driven in areas with winter road salt. Exhaust systems may need replacing. Brake lines corrode and need renewing. The catalytic converter or DPF may fail outright. Multiple simultaneous failures are common, and repair bills can exceed the car's value.

Classic territory (15-20+ years)

Interestingly, failure rates plateau or slightly decrease around the 20-year mark. This is because cars that survive to this age tend to be well-maintained by enthusiasts, or they have been scrapped. Survivors often get careful preventive maintenance that younger 'daily driver' cars do not.

The Repair or Replace Question

At what point does it stop making financial sense to keep repairing an old car to pass its MOT? There is no single answer, but here is a practical framework:

Scenario	Decision
Repair bill under 50% of car value	Usually worth repairing
Repair bill 50-100% of car value	Consider carefully. Get a second quote.
Repair bill exceeds car value	Probably time to replace
Structural corrosion (rust in sills/subframe)	Usually terminal. Welding is expensive and rust returns.

Remember that any replacement car will also have running costs. Compare the annual repair burden of your current car against the total cost of ownership for a replacement, not just the purchase price.

Keeping Older Cars on the Road

Regular servicing: A car serviced annually is far less likely to fail its MOT. Oil changes, filter replacements, and fluid checks prevent the cascade failures that make older cars expensive.
Preventive brake maintenance: Have brake fluid changed every 2 years and brake lines inspected from year 6 onwards. Corroded brake lines are a common, dangerous failure on older cars.
Underseal and rust treatment: Treating the underside of the car with wax-based underseal every 2-3 years can dramatically extend the life of structural metalwork.
Pre-MOT check: Our 20-minute pre-MOT checklist catches the easy failures before the tester finds them.
Choose your garage wisely: A garage that knows your car and has serviced it before is more likely to give fair advice on borderline items than one seeing it for the first time.