Every number Car Ahead shows — the health score, the maintenance predictions, the twelve-month cost forecast, the value estimate and the repair-or-sell verdict — comes from fixed, published rules. There is no hidden model and no guesswork from AI: the same information always produces the same result. This page explains those rules in plain language so you can judge how much weight to give them.

1. Service intervals

The starting point is a list of fourteen common service and wear items, each with a typical interval in both kilometres and months, and a typical European cost range for parts and labour. Examples include the oil and filter service (roughly 15,000 km or 12 months), brake pads and discs (about 45,000 km), brake fluid (about two years), tyres, battery, coolant, timing belt inspection, transmission service and a major scheduled service. Some items only apply to one fuel type, such as a diesel fuel filter or petrol spark plugs.

These intervals are deliberately middle-of-the-road. Manufacturers set their own schedules, which can be shorter or longer, and your service book always takes priority.

2. Your driving

Yearly distance and the share of city driving adjust the intervals. Stop-start traffic and short trips wear brakes, oil and tyres faster, so a high city share shortens those intervals more than, say, the coolant interval. If the yearly distance you enter is implausibly low for the odometer reading, Car Ahead uses a value based on the car’s age and mileage instead.

3. Recorded versus inferred

When you log a service, Car Ahead measures the next due point from that record. When there is no record, it infers where the car probably sits in each cycle from its age and mileage, and says so on screen. Inferred items are never shown as “due this week”, because a guess shouldn’t create false urgency. Logging real service dates is the single best way to make the predictions sharper.

4. Risk levels and the health score

For each item, Car Ahead compares the distance and time since it was last done with its interval. Below about two thirds of the interval the item is fine; then it moves to “monitor”, then “attention”, and past the full interval it becomes high priority. The health score from 0 to 100 starts at 100 and subtracts weighted points for items that are due or overdue — brakes, oil and tyres weigh more than an air filter — and for open issues you have reported. Marking work as done restores the points only because the item is no longer due; there is no artificial bonus.

5. Cost forecast

The twelve-month forecast adds the cost ranges of items expected to fall due within the next year at your driving rate, split into routine servicing, wear parts and larger jobs. Labour-heavy prices are adjusted for your country: labour costs more in, for example, Switzerland or Norway than in Portugal or Poland.

6. Value and depreciation

The value estimate starts from the purchase price if you enter it, or from an average European car if you don’t. Each year the car keeps a share of its remaining value, so the drop is steepest when it is young. Mileage adjusts the result: well above about 15,000 km a year lowers it, well below raises it, within limits. The country then adjusts the price level and the pace of depreciation, because used-car prices genuinely differ across Europe. These country factors are broad approximations, not live market data.

7. Repair-or-sell and keep-or-sell

A repair is compared with the car’s estimated value. Under about 15% of the value the repair usually looks reasonable; 15–35% deserves careful thought; 35–60% is hard to justify on value alone; above that, replacement may be the better option. The verdict also adds expected maintenance over the months you plan to keep the car, and shows the total per month. Keep-or-sell compares the next twelve months of maintenance plus depreciation with the car’s value and its health score.

Where AI is used

AI is only used for three optional extras: the chat assistant (which answers using your car’s data and these same estimates), generating a picture of your car, and reading a VIN. It never sets a score, a prediction or a price.

Limits

  • Car Ahead doesn’t read data from your car and can’t diagnose faults.
  • It can’t see condition, trim, accident history or model-specific weaknesses.
  • Values are estimates, not offers; real prices depend on the specific car and buyer.
  • Safety problems — brakes, steering, tyres, warning lights — need a mechanic now, whatever a score says.

Try the method yourself with the free tools, or read the ownership guides. Questions or corrections are welcome at support.carahead@gmail.com.