Check Your Dashboard Warning Light or Service Indicator
Many modern vehicles display a service reminder on the dashboard when the next service is approaching or overdue. This might appear as a spanner symbol, an oil can icon, a wrench warning light, or a text message in the instrument cluster reading 'Service Due' or 'Oil Change Required'.
Some systems are simple interval-based alerts triggered by mileage or time since the last reset. Others use an oil life monitoring system that calculates remaining oil effectiveness based on actual driving patterns, engine load and ambient temperature. When either type of system triggers a service notification, treat it as a prompt to book promptly — not something to acknowledge once and dismiss.
Consult Your Service Book
Your service book records each service date and mileage with a garage stamp. The most recent entry tells you when and where the last service was carried out. From that entry, calculate forward using the manufacturer's recommended interval: if the last major service was recorded at 24,000 miles and your car now shows 36,000 miles, a major service is due immediately. The same applies to time: if the last stamp is dated eleven months ago, a booking is due very soon.
If your service book shows no entries, or entries that appear inconsistent, treat the vehicle as overdue for a major service regardless of when the previous work may have been done. Starting from a known, documented baseline is always preferable to estimating.
Consult Your Manufacturer's Service Schedule
Your owner's handbook contains a full service schedule specific to your vehicle's make, model and engine type. This is the definitive reference for the correct interval — both in mileage and time — and the type of service required at each stage. Manufacturer recommendations vary considerably: some specify 10,000-mile major service intervals, others 18,000 miles for modern low-friction engines designed for extended-life synthetic oil.
Following the handbook removes guesswork from the calculation and ensures you're using the interval your engine was designed around rather than a generic industry average.
What If You've Bought a Used Car With Unclear History?
Buying a used car without a clear service history makes establishing the correct service timing more difficult. If the previous owner cannot confirm the last service date and mileage, the safest approach is to book a full major service as soon as possible after purchase.
This brings all consumable items up to date from a known, documented point, gives you a clear baseline for all future intervals, and provides peace of mind that safety-critical items — brake fluid, coolant condition, tyre wear, spark plugs — have been properly assessed. It also begins your documented service history from a clear starting point.
What Happens If You Miss Your Service Date?
Driving past a service date by a short period — a few hundred miles or a couple of weeks — is unlikely to cause immediate mechanical damage. But the risk of deferred maintenance increases the further you go beyond the recommended threshold. Engine oil operating past its rated life provides diminishing lubrication. Brake fluid that has absorbed excess moisture has a lower boiling point and reduced effectiveness under sustained braking.
The longer a service is deferred, the more ground needs to be covered when the car is eventually seen — and the greater the probability that something has deteriorated beyond straightforward servicing into a component replacement that could have been avoided with timely maintenance.
How Far in Advance Should I Book?
For a standard service appointment at a busy garage, booking one to two weeks ahead is typically sufficient to secure a convenient slot. For combined MOT and service visits — particularly around busy periods when MOT reminders cluster by registration letter — booking three to four weeks ahead avoids unnecessary delays and ensures parts are ordered and ready for your specific vehicle.
Many garages send annual reminders by email or text when your service is approaching, removing the need to track the date manually. If your current garage doesn't offer this, note the date and mileage from your last service stamp and set a calendar reminder for eleven months ahead — giving yourself a month's notice to book without rushing.