It depends on the size and location of the crack. Damage up to 10mm in the driver's direct line of sight (Zone A) is acceptable, as is damage up to 40mm elsewhere. Anything larger, or anything that obscures the view, will likely be a fail.
It’s one of the most common questions I hear from anxious drivers dropping their car off: "I've got a chip in my windscreen, will it fail its MOT?" It's a fair question. A stone flicking up on the motorway can happen to anyone, and the thought of a costly windscreen replacement on top of any other potential repair work is enough to cause a bit of stress. First, let's get one thing straight: not every crack or chip is an automatic MOT failure. Far from it. The rules are quite specific, and they're designed with a single purpose in mind: to ensure the driver has a clear, unobstructed view of the road ahead. It's all about safety, not about catching you out for minor imperfections. Over my 20+ years as an MOT tester, I've seen everything from tiny starburst chips to cracks that stretch from one side of the glass to the other. In this guide, I'll walk you through the official DVSA rules, explain how we testers actually apply them in the real world, and give you some honest, practical advice on what to do if your windscreen is less than perfect. My goal is to demystify the process so you can approach your next MOT with confidence.
The official UK MOT rule
Right then, let's get down to brass tacks. The rules we follow come directly from the DVSA's 'MOT inspection manual for private passenger and light commercial vehicles'. The bit we're interested in is Section 3, which covers 'View to the front'. Specifically, item 3.2: 'Windscreen'. The manual is very precise and splits the windscreen into two distinct areas. This is the most important thing to get your head around: * **Zone A:** This is a 290mm wide vertical strip, centred on the steering wheel. It's essentially the driver's direct line of sight, the critical area you look through for the majority of your driving. Think of it as the width of your steering wheel, extended all the way up the windscreen within the area swept by the wipers. * **The Rest of the Windscreen:** This is simply everything else on the screen that is swept by the wiper blades. With these zones in mind, the rules for failure (a 'Major' defect) are quite straightforward: 1. **In Zone A:** Any damage (a chip, crack, or even significant scratching) that is larger than **10mm** in diameter is a fail. It doesn't matter if it's a single crack or a cluster of damage; if the whole affected area is more than 10mm across, it's a no-go. 2. **In the Rest of the Swept Area:** Any damage larger than **40mm** in diameter is a fail. So, a 10p coin is about 24.5mm wide, and a £2 coin is 28.4mm wide. This gives you a good real-world reference. A tiny chip in front of you that you could cover with the nail on your little finger is likely fine. A crack the length of your thumb, on the other hand, is definitely not. There's one more crucial point the manual makes: the tester must also fail a vehicle if 'the driver’s view of the road is significantly affected'. This is a bit more of a judgement call, but it covers things like a web of cracks or heavy scratching that might individually be within limits but collectively make it hard to see. It also covers any damage that could interfere with the wipers, like a sharp e
How testers actually assess this
Reading the manual is one thing, but what actually happens when your car is in the test bay? Let me walk you through my process for checking a windscreen. It's a physical, hands-on check, not just a quick glance from outside the car. First, I sit in the driver's seat, exactly where you would sit. This is vital, because I need to see the world from your perspective. I'll look for any obvious chips, cracks, or cloudy areas. I'm especially focused on that critical Zone A, directly in front of my eyes. If I spot anything, my next step is to measure it. We have official DVSA-approved tools, which are basically small pieces of transparent plastic with circles printed on them – one 10mm and one 40mm. I'll place this over the damage to get a definitive measurement. There's no guesswork involved; either it fits inside the circle, or it doesn't. If the damage is larger than 10mm in Zone A or 40mm elsewhere, it's logged as a Major defect, and that's a fail. But it's not just about size. I also need to assess the *type* of damage. I'll run my finger over the outside of the screen. Does the crack have a sharp edge that could catch and tear a wiper blade? If so, that's a problem. I'll then switch on the ignition and operate the windscreen wipers with the washers. I'm watching to see if the wipers sweep smoothly over the damaged area. If a blade judders, lifts, or smears water across the driver's view because of the crack, that can also be grounds for failure, as it means the screen can't be properly cleared. I'm also looking for what we call 'visual intrusion'. Is the crack splintered in a way that catches the light and creates a distracting starburst effect? Is there discolouration or cloudiness around the damage from a previous, poor-quality repair? The rulebook gives us leeway to fail anything that 'significantly affects the driver's view'. A 9mm chip that's perfectly within the size limit could still fail if it creates a prism effect that's genuinely distracting to the driver
Common scenarios — pass, advisory or fail?
Theory is all well and good, but let's look at some real-world examples that I see almost every week. This should give you a much clearer idea of where your own windscreen might stand. * **Scenario 1: The tiny stone chip.** A lorry kicks up a stone on the A1 and leaves a small, 6mm 'bullseye' chip right in the driver's line of sight (Zone A). Is it a fail? **No, this is a Pass.** The damage is well within the 10mm limit for Zone A. I would, however, strongly consider adding an 'Advisory' notice to the MOT certificate. This would say something like "Nearside front windscreen has a stone chip". This doesn't affect your pass certificate, but it's a formal heads-up that you have damage which could spread into a larger, failing crack if you hit a pothole or the temperature changes suddenly. It's my way of saying, "Get this sorted before it becomes a real problem." * **Scenario 2: The growing crack.** A crack has started from the edge of the passenger side and has now crept to be 35mm long. It's well outside Zone A. Is this a fail? **No, this is a Pass.** The damage is within the 40mm limit for the 'rest of the swept area'. Again, I would almost certainly issue an advisory here, because a 35mm crack is on its way to becoming a 40mm+ failing crack. * **Scenario 3: The obvious fail.** A star-shaped chip in the middle of Zone A measures 15mm across at its widest point. Is this a fail? **Yes, this is a definite Fail.** It is damage greater than 10mm within Zone A. There's no grey area here; it's a clear-cut 'Major' defect according to the manual. The car cannot be driven (except to a repairer) until it's fixed. * **Scenario 4: The long runner.** A single, clean crack runs from the bottom of the windscreen up towards the middle, measuring 60mm in length. Is this a fail? **Yes, this is a Fail.** It doesn't matter where this crack is located in the swept area; at 60mm, it exceeds the 40mm maximum limit for damage outside of Zone A. * **Scenario 5: The obscured view.** The windsc
What to do if you're worried before your test
If you've read this far and you're still a bit worried, don't be. There are simple steps you can take before you even book your MOT. First, do your own inspection. It's easy. Sit in the driver's seat and get a feel for where Zone A is. Remember, it's a 290mm wide band centred on the middle of your steering wheel. Use a ruler if you're unsure. Now, grab a coin. A 5p piece is about 18mm wide, and a penny is 20mm wide. Use these as a rough guide. A tiny chip that looks smaller than your little fingernail is almost certainly under 10mm. If you find a chip, measure it as best you can. If it's in Zone A and looks bigger than 10mm, or if it's elsewhere and looks bigger than 40mm, it's very likely going to be a fail. A lot of people bring their car in hoping for the best, but if the damage is clearly outside the limits, it's always better to sort it beforehand. Why? Because repairing a small chip is often much, much cheaper than replacing the whole windscreen. Many insurance policies include windscreen cover with a very small excess (sometimes free!) for repairs, whereas a full replacement might have a larger excess of £75-£150. A chip repair specialist can inject a special resin into the chip, which is then cured with UV light. This makes the chip almost invisible and, crucially, restores the structural integrity of the glass, preventing the chip from spreading into a crack. If you have a chip, even a small one that you think will pass, it's always wise to get it repaired. It removes all doubt for the MOT and prevents a sudden temperature change (like using your air-con on a hot day or de-icing on a cold one) from turning a £20 repair job into a £500 replacement job overnight.
What happens if you do fail
Let's say the worst happens and I have to fail your car on its windscreen. Please don't panic or worry – it's a common failure, and the process for putting it right is very clear. First, I will complete the test and then issue a VT30 'Refusal of an MOT Test Certificate'. This document will clearly list the defect – for example, "Windscreen has damage in excess of 10mm in Zone A". This is your official notification of the failure. At this point, your car may not have a valid MOT. If your old MOT certificate is still valid (i.e., you brought the car in for its test early), you can still drive the car until that certificate expires. However, if your old MOT has expired, you can **only** legally drive the car to a pre-booked appointment to have the windscreen repaired, or to a pre-booked MOT retest after the repair is complete. Driving it for any other reason (like going to the shops or to work) could land you in serious trouble with the police. Your best bet is to arrange for a mobile windscreen replacement service to come to your home or the garage. Once the new screen is fitted, you can bring the car back for a retest. The good news is that for just a windscreen failure, you're entitled to a 'partial retest'. If you bring the car back to the **same test station** before the end of the next 10 working days, the retest is often done for free or at a reduced rate (usually half the full test fee). I'll just need to check that the windscreen is new and the issue is resolved, and then I can issue your pass certificate (a VT20). While a new windscreen isn't cheap, it's a straightforward fix. Check your insurance documents first, as you are very likely covered. The most important thing is not to be tempted to drive with a failed, dangerous windscreen. It's not worth the risk.
Can I repair a chip myself before the MOT with a DIY kit? — You can, but I'd advise caution. DIY kits from car accessory shops can be a bit hit-and-miss. They can sometimes trap air or moisture, leading to a cloudy finish that still obstructs your view. A professional repairer uses a vacuum-sealed process to inject the resin, which gives a much clearer and stronger result that's far more likely to be invisible to an MOT tester. For the sake of avoiding a potential fail and retest fee, getting a professional to do it is usually the safer bet.
Does a cracked windscreen give me penalty points on my licence? — Failing the MOT itself does not result in penalty points. However, the MOT fail confirms that your vehicle is unroadworthy. If you are stopped by the police while driving with a windscreen that is cracked to a point of being dangerous, you can be prosecuted for driving a vehicle in a dangerous condition. This can lead to a fine of up to £2,500 and three penalty points on your licence. This is why it's illegal to drive with a failed MOT, except to a pre-booked repair.
What about damage on the passenger side or at the very top of the windscreen? — The key thing to remember is the two zones. If the damage is on the passenger side, it falls into the 'rest of the swept area', where damage up to 40mm is allowed. This is quite a large area, about the size of a golf ball. Damage outside the area swept by the wipers altogether (like right at the very top edge or a blacked-out border) is not considered part of the test, as it doesn't obscure your view of the road.
Is a broken heated windscreen element an MOT fail? — No, a non-functioning heated windscreen is not an MOT test failure. The MOT rules for 'view to the front' are concerned with your ability to keep the screen clear using your wipers and washers. As long as the washers spray and the wipers clear the water effectively, that's a pass for that item. The heating elements, along with your air conditioning, are considered creature comforts and are not part of the mandatory safety inspection. So, you can relax on that point!