Windscreen chips and cracks on your MOT: the 10mm and 40mm rules
A windscreen chip fails the MOT if it's more than 10mm across in zone A, the strip directly in front of the driver, or more than 40mm across anywhere else in the area the wipers clear. Anything smaller is usually an advisory or nothing at all. Get small chips repaired quickly, because a chip that spreads into a crack generally can't be repaired and the whole screen has to be replaced.
What zone A is
Zone A is a 290mm-wide band on the windscreen, centred on the steering wheel and running up the screen within the area the wipers sweep. It's the part of the glass you look through most when driving, so the rules are tightest there.
| Where the damage is | MOT fail if bigger than |
|---|---|
| Zone A (290mm band in front of the driver) | 10mm |
| Rest of the area the wipers clear | 40mm |
| Outside the swept area | Only if it seriously affects the driver's view |
The test is about the driver's view of the road. Damage that's within the limits but still bothers the view can be noted, and damage on the passenger side is treated more generously.
What the advisory means
If you've got a windscreen advisory, the tester saw damage that's within the limits. It might be a small chip, a few scratches or a stone mark. The MOT categories here are:
- Damaged or discoloured glass that doesn't affect the driver's view: minor.
- Damage that affects the driver's view of the road or of a required external mirror: major (fail).
- Glass in a condition that seriously affects visibility through the swept area: dangerous.
A chip that's been properly repaired and is flush and barely visible isn't treated as damage, as long as it doesn't interfere with the view.
Repair or replace?
Most small chips can be filled with resin. It stops them spreading and usually leaves a faint mark. Repairers generally won't fix a chip that's too big, sits right on the edge of the glass, or has already started to crack, and some won't repair damage in the driver's main line of sight.
| Option | Rough cost |
|---|---|
| Chip repair | Often free or cheap through windscreen cover on your insurance, otherwise around £50 to £80 |
| Screen replacement, older car | £200 to £400 |
| Screen replacement with camera recalibration | £400 to £800 or more |
Many newer cars have a camera behind the windscreen for lane keeping or emergency braking. After a new screen goes in, that camera usually needs recalibrating, which adds to the cost. Check your policy before paying out of pocket. A lot of car insurance policies include windscreen cover, sometimes with a small excess for replacements.
Stopping a chip from spreading
- Get it repaired within days if you can. Dirt and moisture get into chips and make repairs less clear.
- Put a bit of clear tape over it in the meantime to keep water and grit out.
- Avoid blasting hot air onto a frozen screen, or pouring hot water on it. Sudden temperature changes are what turn chips into cracks.
- Close doors gently. A hard slam flexes the glass.
What to do now
Measure the chip. If it's in front of the driver and anywhere near 10mm, sort it before the next MOT. Then check whether your insurance covers repairs. For the rest of your result, paste it into the MOT advisory decoder to see everything in order of urgency.
Got more than one advisory?
Paste your whole MOT result into the decoder. It explains every line, sorts them by urgency and adds up a rough repair budget.
Decode my MOT