Car service intervals: interim, full and major explained
By James Snow
Owner and mechanic, SV Autos
Updated 25 July 2026
Booking a service and not knowing which one you actually need is a common spot to be in, and garages don't always explain the difference. There are three levels you'll usually see: interim, full and major, and each does a bit more than the last. Here's what each one covers, how often they're due, and why the exact timing depends on your car more than any general rule.
The interim service: the little-and-often one
An interim service is the lighter check that keeps things ticking over between the bigger ones. The core of it is an oil and filter change, plus a look over the safety items that wear or move: brakes, tyres, lights, wipers, fluid levels and the like.
It's typically done every six months or around 6,000 miles, whichever comes first, and it suits cars that cover a lot of miles or do a lot of short stop-start trips. Think of it as topping up the maintenance rather than the full going-over.
- Engine oil and oil filter changed
- Brakes, tyres, lights and wipers checked
- Fluid levels topped up (coolant, screenwash, brake fluid and so on)
- A general look over for anything obviously wrong
The full service: the yearly going-over
The full service is the one most people mean when they say their car is 'due a service'. It includes everything in the interim, then adds a longer list of checks and usually a few more parts, such as the air filter, along with a more thorough inspection of the suspension, steering, exhaust and drivetrain.
It's typically done once a year or around every 12,000 miles, whichever lands first. For most cars doing an average mileage, a yearly full service is the sensible baseline that keeps the car healthy and the history intact.
The major service: the deeper one
A major service is a full service with extra items on top: the parts and fluids that don't need doing every year but do wear out over a longer stretch. That often means things like the fuel filter, spark plugs (on petrol cars), cabin/pollen filter and fluid changes.
It's typically due every couple of years, sitting on top of the yearly rhythm rather than replacing it. Because it swaps out more of the consumable parts, it's the one that resets the car most thoroughly.
Time or mileage: whichever comes first
Every interval works on two clocks at once: the calendar and the odometer. Whichever one you hit first is when the service is due. A high-mileage driver hits the mileage figure long before the year is up, and a car that barely leaves the drive hits the time limit while the mileage is still low.
That second case catches people out. Oil degrades with age and with heat cycles, not just with miles, so a low-mileage car still needs its oil changed on time. Don't skip a service just because the clock hasn't turned many miles.
Your handbook is the real authority
The interim, full and major labels are the industry's way of describing service levels, but they aren't set by your manufacturer. What your specific car needs, and when, is laid out in its own service schedule in the handbook.
Some cars want a fresh cambelt at a set age or mileage, some use a long-life oil on a longer interval, some flag the service on the dashboard themselves. Cambelt intervals in particular vary a lot between makes and models, so that's one to check against the schedule rather than guess. When we service a car, we work to what the manufacturer sets for that model, not a one-size-fits-all list.