Most of us have been there. You spot a tiny chip on your windscreen, tell yourself you’ll deal with it later, and carry on with your day. It doesn’t look serious. It isn’t blocking your view. And nothing seems to change for a while.
But windscreens don’t stay the same for long. A small chip can turn into a long crack without much warning. Temperature changes, potholes, or even shutting a door a bit too firmly can make the damage spread.
So how risky is it really? And when is it time to stop driving and get it sorted? This guide explains the safety concerns, UK MOT rules, and insurance issues that come with cracked windscreens.
Why does a cracked windscreen matter so much?
Your windscreen is a key safety feature of your car. Modern windscreens are made from laminated glass, which means two layers of glass with a plastic sheet in the middle. This design helps the windscreen stay in one piece during impact.
A healthy windscreen does three important jobs.
It keeps the structure of the car strong.
In a crash, the windscreen helps stop the roof giving way. If the glass is weakened by cracks, it’s less able to carry that load.
It supports the airbag.
In many cars, the front passenger airbag actually pushes against the windscreen as it inflates. If the windscreen gives way, the airbag may not work as it should.
It keeps your vision clear.
A crack might not seem distracting at first, but light can catch the edges and distort what you see. Even a small mark can affect your reaction time.
When you think about it like that, you can see why ignoring a crack isn’t something to take lightly.
How do small chips turn into bigger cracks?
Most cracks start out as tiny stone chips. A bit of grit hits the glass while you’re driving and leaves a mark about the size of a fingernail. It looks harmless.
But a few things can make that chip grow:
• Cold mornings and warm heaters
Heating the glass from the inside while the outside stays frozen creates stress. That stress often makes chips travel in long lines across the screen.
• Potholes and speed bumps
Any sharp jolt sends vibrations through the car. That’s sometimes enough to turn a small chip into a spreading crack.
• Hot sun
On warm days, the glass expands. If it expands unevenly, cracks form or get worse.
• Moisture
Rainwater can seep into a chip and freeze overnight, forcing the damage to spread further.
Windscreens are under constant pressure, so problems rarely stay the same for long.
If you want to know exactly when damage goes beyond a simple repair, have a look at: At What Point Does Windscreen Damage Require Full Glass Replacement?
Is it safe to drive with a cracked windscreen?
It depends on the size and where the crack is. But in general, if it distracts you, if it sits in your direct field of vision, or if it’s longer than around 4cm, your car might not be safe to drive.
Here are a few useful guidelines.
- If the crack is directly in front of the driver
Any damage larger than 10mm in what the MOT calls “Zone A” (the area roughly the width of the steering wheel) can be dangerous. Even small cracks here can distort your view. - If the crack is elsewhere on the windscreen
Damage up to 40mm may still be repairable, but if it’s bigger than that, replacement is usually the only option. - If the crack is spreading quickly
That’s a sign the glass has lost its strength. Driving with fast-spreading damage isn’t recommended.
Will a cracked windscreen fail an MOT?
Yes, it can. Windscreen condition is part of the official MOT test in the UK. The tester checks for chips, scratches, and cracks that could affect the driver’s view.
The rules are clear and straightforward:
In the driver’s central view (Zone A)
Any damage larger than 10mm will result in an MOT fail.
In the rest of the windscreen
Any damage larger than 40mm will also lead to failure.
Even if the crack is slightly under these limits, testers may still judge that it restricts visibility. That could mean an advisory, which is the MOT’s way of saying “you need to sort this out soon”.
If your MOT is coming up, it’s worth fixing any damage beforehand. It avoids the hassle of a failed test and means you won’t be without your car.
Could a cracked windscreen affect my insurance?
In many cases, yes. It can affect you in three different ways.
Your insurer may refuse a claim if they think the car wasn’t roadworthy.
If you have an accident and your windscreen was badly cracked, the insurer might argue that the damage played a part. That could reduce or even invalidate a claim.
Your windscreen cover might not apply if the damage becomes worse through delay.
Most policies encourage quick repairs. Leaving damage for months can be seen as neglect, which may limit what your insurer pays out.
You might have to pay more for a full replacement.
A simple chip repair is usually cheap or even free through windscreen cover. A full replacement is more expensive and often comes with an excess.
If you’re ever unsure what your policy covers, a quick call to your insurer can save surprises later on.
If you’re unsure how a windscreen claim might affect your no-claims bonus, take a look at “Will a Windscreen Claim Affect Your No-Claims Bonus? Everything You Need to Know.”
How do I know if my windscreen needs repairing or replacing?
It usually comes down to size, depth, and location.
A windscreen repair is often possible if the damage:
• is smaller than a 10p coin
• is not in the driver’s direct line of sight
• has not cracked all the way through
• has clean edges that haven’t filled with dirt or moisture
A replacement is usually needed if:
• the crack is longer than 40mm
• the damage sits directly in front of the driver
• the crack has reached the edge of the windscreen
• the glass is visibly weakened or flexes when touched
Repairing a chip early can save the whole windscreen. The resin used in repairs can restore most of the strength and stop the crack from spreading.
If you’re still unsure what your windscreen needs, you might find our guide “How to Tell If You Need Windscreen Repair or Replacement” helpful.
What should I do if my windscreen cracks while driving?
It can be alarming when you hear that sudden sharp “pop”. If it happens, stay calm. Cracked windscreens don’t collapse instantly due to the laminated glass design.
Here’s what to do:
- Check your view.
If you can still see clearly and the crack isn’t spreading rapidly, it’s normally safe to continue your journey. - Avoid sudden temperature changes.
Don’t blast the heater or air conditioning at the glass. - Drive gently.
Avoid rough roads and heavy bumps if you can. - Arrange a repair as soon as possible.
The sooner you deal with it, the less likely it is to get worse.
How quickly should I get a windscreen chip repaired?
Ideally, within a few days. Chips almost always get bigger, and the cost of repair is usually small compared with replacement.
A quick repair can also keep your insurance record clean, avoid MOT issues, and maintain your car’s safety. Waiting rarely saves money, and in most cases, it ends up costing more.
Can I fix a cracked windscreen myself?
DIY kits exist, but they’re not recommended for anything more than tiny, shallow chips. Even then, the results are often mixed.
A poor repair can trap air or moisture inside the crack, making it more noticeable and harder to fix later. It may also affect MOT visibility rules. Professional repairs use stronger resin and vacuum-based equipment to ensure a clean, durable bond.
If the damage is big enough for you to worry about, it’s big enough to let an expert handle it.
Need help with a chipped or cracked windscreen?
If you’ve noticed damage and you’re not sure what to do next, we’re here to help.We look at these problems every day, and we can quickly tell you whether your windscreen is still safe to drive with or if it needs a simple repair.
Call us on 01279 870 001 for a free quote!