Windscreen Damage and MOT: Chips, Cracks, and Failure Zones

A chip or crack in your windscreen is one of those problems that can feel minor one day and critically important the next — particularly when your MOT is approaching. Understanding the precise windscreen damage MOT rules can save you from an unexpected failure and help you decide whether to book a repair before your test. This guide explains the zones, the size limits, and the common mistakes drivers make.

How the MOT Windscreen Zones Work

DVSA testers assess windscreen damage by dividing the glass into two distinct zones. Zone A is a centrally positioned band, 290 mm wide, that sits directly in front of the driver and aligns with the swept area of the windscreen wiper. Zone B covers the remainder of the wiper-swept area beyond Zone A.

The rules differ significantly between the two zones. In Zone A, any damage that is larger than 10 mm in diameter will result in an MOT failure. In Zone B, the limit is more generous — damage must exceed 40 mm before it constitutes a failure. Damage outside the swept area entirely is unlikely to cause a fail on its own, though a tester may still note it as an advisory if it risks spreading or impairing visibility in poor conditions.

It is also worth noting that even small chips in Zone A can fail the test if they cause distortion, starred cracking, or a reflection that dazzles the driver. The tester has discretion here, so a repaired chip that still shows slight distortion may still be flagged.

Chips vs Cracks: Is There a Difference Under MOT Rules?

Many drivers assume that a hairline crack is treated differently to a bullseye chip. In practice, the same size rules apply — what matters is the width, length, and location of the damage, not strictly its shape. However, cracks tend to grow faster and more unpredictably than chips, so testers will look carefully at whether a crack sits near the edge of the glass (where pressure is greatest) or whether it is already extending towards Zone A.

A crack running through Zone A that is visible to the tester, regardless of width, is very likely to result in a failure on the grounds of obscured or impaired vision. The DVSA guidance states that the tester must consider whether the damage would adversely affect the driver's view of the road — and a crack across the primary line of sight almost always will.

Common Windscreen MOT Failures and How to Avoid Them

Many windscreen-related MOT failures are entirely preventable. The most frequent causes include:

• Leaving a chip unrepaired until it cracks — a small chip in Zone B can spread into Zone A during cold weather or after a pothole impact.
• DIY chip repair kits leaving visible distortion — these kits can seal a chip but the resin may create a haze or bubble that a tester will flag.
• Wiper blade damage creating scratches — deep scratches caused by a worn or gritty wiper blade across the driver's line of sight can be treated as obscured vision.
• Stickers or sat-nav mounts obstructing Zone A — anything attached to the glass inside Zone A that restricts the driver's view is a failure point.

The simplest preventative step is to get any chip repaired by a professional as soon as it appears. Most chips cost under £30 to fix and the repair is usually covered by comprehensive car insurance without affecting your no-claims bonus. Delaying a repair to save money often results in a more expensive replacement and a failed MOT.

Windscreen Replacement Before an MOT: Is It Worth It?

If a crack has already spread across Zone A, or the damage exceeds the Zone B limit, you will need a full windscreen replacement rather than a repair. The good news is that a new windscreen fitted by a reputable technician will almost certainly pass the windscreen element of the MOT. However, timing matters — if the adhesive used to bond the new screen has not fully cured before the test, the screen could still be considered unsafe.

Most modern windscreen adhesives cure within one to two hours for driving, but full structural cure takes 24 hours. If you have a screen fitted the day before your MOT, inform the tester so they can factor this in. In practice, the vast majority of replacement screens pass without issue.

Checking your MOT history before buying a used car is always worthwhile — a pattern of windscreen advisories across multiple years can indicate a car that has been repeatedly neglected in this area.

What Happens If You Drive With a Failing Windscreen?

Driving with a windscreen that would fail an MOT is not just a test issue — it can be a legal one. Under the Road Traffic Act 1988, it is an offence to use a vehicle in a dangerous condition. A cracked windscreen that significantly obstructs the driver's view could constitute a dangerous condition, potentially resulting in a fixed penalty notice, points on your licence, and in serious cases, prosecution.

Insurance is also a consideration. If you are involved in an accident and your windscreen was in a condition that would have failed its MOT, your insurer may argue that the vehicle was not roadworthy and attempt to reduce or void your claim. The financial risk of ignoring windscreen damage far outweighs the cost of a repair.

Checking Your Car Before the MOT

Windscreen condition is one of the easiest things to check yourself before booking your MOT. Stand outside the car on a bright day and look across the glass at a low angle — chips and cracks become much more visible this way. Identify where any damage falls relative to the driver's seated position and the wiper sweep zone.

You can also review your car's full MOT history to see whether windscreen issues have been noted as advisories in previous years. If windscreen damage has appeared regularly, it may be worth budgeting for a full replacement.

For a broader view of your car's test readiness, run a quick MOT check to see when your current certificate expires and what failures or advisories were recorded last time. Understanding your car's history puts you in a much stronger position heading into any test.