Car health score: how it's calculated, and why it sometimes shows nothing
Updated · Autofy
Car health score: how it's calculated, and why it sometimes shows nothing
A car health score out of 100 is a weighted average of the condition of the parts you have actually logged: a timing belt or brakes count far more than a cabin filter. Parts you never entered are not guessed at — they lower the precision instead, and below a certain precision no number is shown at all. An urgent engine or brake fault caps the verdict, whatever the service history says.
Why most car scores are wrong
A car "health score" sounds simple: average the condition of the parts. Two things make that average lie.
Not every part matters equally. A timing belt that snaps can destroy an engine. Worn wipers are an annoyance. Giving them the same weight produces a number that looks precise and means nothing.
An unknown part is not a half-healthy part. If a tool counts a never-logged part as "50 %", it invents data. On a brand-new account the score is then pure noise — shown with the confidence of a measurement.
Autofy's score is built around two separate questions that should never be mixed:
- The score: how good is what we know?
- The coverage: how much of the car do we know?
How each part is weighted
The weight of a part is what happens if you neglect it. The ranking follows the severity of the failure, not taste:
| Weight | Parts | Why |
|---|---|---|
| Highest | Timing belt, brakes | A failure can destroy the engine or remove your ability to stop |
| High | Engine oil, tyres | Neglected long enough, they kill the engine or the grip |
| Medium | Technical inspection | Without it the car can no longer legally be driven |
| Lower | Battery, brake fluid, coolant | Immobilising or costly, but often recoverable |
| Lowest | Oil, fuel, air and cabin filters | They affect consumption and comfort more than safety |
Autofy tracks 12 parts in total. Brake fluid and coolant are in that list on purpose: unlike a scraping wiper blade, neither warns you before it costs you the brakes or the engine.
A part with margin is a healthy part
An earlier approach took the "remaining life" of a part literally: an oil change done halfway through its interval counted as 50 %. The absurd result was a perfectly maintained car losing half its score simply because time was passing.
A part with a comfortable margin is healthy, full stop. Points are only lost as the due date approaches, and again once it is passed. An overdue critical part (belt, brakes, oil, tyres) costs a little more on top, with a cap so one neglected item doesn't flatten everything.
Brake pads are a special case: they wear with braking, not with the calendar. Past their reference period they read "worth a check", never "overdue" on date alone (see when to replace brake pads).
Faults and warning lights
An open fault costs points according to the system it touches, not the mood of the moment. A faulty electric window costs a point or two; an injector fault costs several times more. Marking a fault "urgent" raises its cost but never beyond what the system justifies: you can adjust the score, you can't decide it. The total is capped, so declaring five faults doesn't send the score to zero and punish exactly the person who is being honest.
Resolving a fault removes its cost immediately.
The driver-sense rules
Some rules exist because a purely mathematical score can disagree with common sense:
- An urgent engine or brake fault forbids "good". Whatever your service history says, the verdict stays below 50 until the fault is resolved.
- A vital part never logged on a high-mileage car can't be "excellent". A car with 140,000 km whose timing belt is unknown can't be promised as excellent — we don't know, so we don't promise.
- The score stays silent when precision is too low. Below roughly a third of the car's weighted parts, Autofy shows no number rather than an invented one.
The verdict bands: excellent from 75, good from 50, worth watching from 30, critical below.
What to do with it
The score is a compass, not a mechanic. It tells you which part to look at next; your carmaker's service schedule remains the reference. To see when your next service falls due, use the free maintenance calculator, or read how to choose a maintenance app.
Autofy computes this score on your phone for the parts you log — free for one vehicle.
Frequently asked questions
What does a health score of 100 mean? That everything the app knows about your car is in good order. It is not a promise about the parts you haven't logged, which is why Autofy also shows how much of the car it actually knows.
Why doesn't my score show a number yet? Too few parts have been logged. A number built on almost nothing would be noise displayed with the confidence of a measurement, so the score waits until the parts that matter (oil, tyres, brakes…) are filled in.
Does the score drop just because time passes? No. A part with a comfortable margin is healthy. Points are lost as its due date gets close, and again once it has passed.
Can a well-serviced car still get a low score? Yes, if an urgent fault on a vital system such as the engine or the brakes is open. The verdict stays below "good" until that fault is resolved.