Timing belt interval calculator
Two limits govern a timing belt: a mileage figure and an age figure. Whichever arrives first is the one that counts, and on most cars driven normally it's the age figure — years before the odometer gets anywhere near.
Why the years usually get there first
A cambelt is rubber with cords running through it. It doesn't only wear from turning — it hardens, and heat cycles, oil vapor and simply sitting still all age it. That's why manufacturers publish two limits rather than one, and why a low-mileage car isn't automatically a safe car.
Run the numbers on an average European or American driver at roughly 12,000 miles a year against a 100,000-mile, six-year interval, and the belt is due at 72,000 miles. The mileage limit never comes into it. The cars that get caught out are the ones bought second-hand on low mileage, where the seller says the belt "has barely done any miles" — which is true, and irrelevant.
For what the job itself costs, we broke it down by engine layout in timing belt replacement cost by engine type.
If yours is a wet belt, the interval is only half the story
A wet belt sits inside the engine, bathed in oil. That changes the failure mode: the belt sheds material into the sump, and the debris blocks the oil pick-up screen. The engine then dies of oil starvation, which is a far bigger bill than a snapped belt on an interference engine.
Two things follow. The published interval on these engines has been revised downward more than once, so the figure in an older manual may no longer be the figure the manufacturer stands behind — worth checking against the latest service schedule. And the oil specification stops being a detail: the wrong oil accelerates belt breakdown directly. We covered that in the oil a wet belt engine actually needs.
Engines we've confirmed use a wet belt: Ford 1.0 EcoBoost, Ford EcoBlue diesels, and the PSA/Stellantis PureTech 1.0 and 1.2. The full picture, including how to identify one on a car you're looking at, is in wet belt engines explained.
Why the engine list has two entries on it
Because those are the two whose current published interval we've actually checked, across more than one source, with the working written down. A dropdown offering forty engines would look far more useful and would be mostly guesswork — and a guess about a belt is worse than no answer, because it's an answer somebody acts on.
The list grows as engines get verified, not as they get typed in. Until yours appears, the manual entry above is the honest route, and it's what the calculator was built around.
One thing worth taking from the two that are on it: both were revised downward. Ford went from 150,000 miles and 10 years to 100,000 and 6. Stellantis went from around 175,000 km to 100,000. If your handbook was printed before the revision it still shows the old figure, nothing in the car tells you it moved, and the shortfall is measured in years.
What this calculator doesn't do
It doesn't know your car. Past the two verified engines above there's no database and no lookup by registration — it works on the numbers you type in, which is why the interval has to come from your manual rather than from us.
It also can't see the belt. Age and mileage are the two limits that get published, but a belt contaminated by a leaking cam seal, or one fitted badly last time, can fail well inside both. If the car is near either limit, the calculator tells you to have it looked at rather than pretending arithmetic settles it.
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