Car insurance write-off categories can be intimidating for the uninitiated. Writing off a car is up there among every motorist's worst nightmare: you have a minor prang, and a few days later your insurer calls you to say that the damage isn't economically worth repairing, and your car needs to be written off.

This can be deeply frustrating, especially when the damage looks to be cosmetic and has no bearing on either the car's roadworthiness or its resale value. If a car is worth £500 and you crack the front bumper, the chances are your insurer won't pay for a repair or replacement part. As a rule of thumb, your car is likely to be written off if a professional repair costs more than half of its value.

Don't lose hope though: there are different levels of insurance write-off and you won't always need to part ways with your car. And if you're a buyer, just because a car has been written off doesn't necessarily mean you should steer clear.

What is Cat A, Cat B, Cat S or Cat N insurance write-off?

There are four categories of car insurance write-offs. The system was revamped in October 2017, with new denominations given to the categories at the lower end of the damage scale. This can be confusing if you're not sure what the letters mean, so let's explain them.

Category A

Reserved for the most severely damaged vehicles, a Category A write-off condemns an entire vehicle to the scrapyard, and means not even seemingly serviceable parts can be repurposed.

High-speed impacts, complete burnouts and extensive vandalism will usually result in a vehicle receiving a Category A designation.

Category B

The Category B write-off is reserved for cars that have received extensive damage - be it structural, mechanical or electrical - and cannot be put back on the road.

While the car’s shell must be crushed to avoid it being used again, serviceable parts can be removed from Category B cars and used on other vehicles. Only Authorised Treatment Facilities (ATF) are permitted to handle Category B vehicles, and will only sell them to businesses that have certification to prove they are allowed to store and destroy such vehicles.

Category S

Formerly called Category C, Category S write-offs encompass vehicles that have received structural bodywork damage - a bent chassis or creased door frame, for example - but that can be repaired and put back on the road. 

It’s important to note that, although a Category S write-off is among the least severe, the vehicle will be deemed unsafe for use until it has been professionally repaired.

Category N

The designation named Category N write-off replaced the old Category D and is used to describe vehicles that have received non-structural damage that the insurer has deemed not worth repairing. 

Though the damage may be less visibly severe than a Category S write-off, ‘non-structural damage’ could affect the electronics, brakes, suspension or mechanics of a car, so it will still usually need rectifying before it goes back on the road. 

As it is normally relatively easy to repair this level of damage, many Category N write-offs can be found in the classifieds, and shouldn’t cost much more to insure than a non-damaged car. 

What happens after a write-off?

When an insurer is notified that a vehicle has been damaged, it will assess the damage to determine whether it should be written off, and to what extent. 

An insurer will offer the owner an agreed market value for the damaged vehicle and take legal possession of it until it is sold or scrapped. If the owner wishes to keep the vehicle - whether because it is only a Category N write-off and it can still be driven, or because they are able to repair the damage for less than the cost of a replacement - they can refuse the offer and keep the car. 

In all cases, the DVLA must be notified of the write-off, and will need to assess any repairs made to a Category S car before it returns to the road. Given the usually superficial nature of Category N damage, it does not require further assessment, but must still be kept in a roadworthy condition. 

Should you buy a written-off car?

Category A write-offs go straight to the crusher, and cannot be purchased or put back on the road, but you will often find Category B cars being ‘broken’ for parts in the classifieds. You are unable to buy the whole vehicle (the shell must be scrapped) but can purchase individual components if they are still in a serviceable condition.

As for Category N and Category S cars, buyers must thoroughly inspect the standards of any repair work carried out, and take the time to ensure that they know exactly how the damage occurred. 

Comprehensive vehicle history checks aren’t free, but could save buyers a fortune in repairs down the line, and given a written-off car is likely to be discounted, the extra outlay is negligible. 

Can a written-off car be insured?

Insurers are naturally wary of write-offs, because they’re taking a risk on any non-factory-standard repairs that might have been made, and so premiums are often higher. 

An insurance company can insist that an independent engineer inspects the vehicle before it agrees to provide cover, though an MOT certificate can also be used as proof of roadworthiness. 

Some insurers won’t ask about a vehicle’s crash history when providing a quote, but will check the records in the event of a subsequent accident to ensure a poorly carried out repair wasn’t a factor.