An idling engine does zero miles per gallon, and ten minutes of it a day costs roughly £100 to £145 a year at September 2026 prices. The exact figure depends on your engine and fuel: typical consumption while idling is quoted at 1.0 to 1.5 litres an hour for a 2.0-litre engine, which adds up to 60 to 90 litres a year for a daily ten-minute habit.
- Ten minutes of daily idling burns roughly 60 to 90 litres a year.
- At 161.2p petrol that is £97 to £145; diesel is dearer still.
- Restarting a modern engine costs about 10 seconds of idling fuel.
- The warm-up idle is the biggest single waste - engines warm faster driven gently.
The zero mpg problem
When your car is running but not moving, you are achieving exactly zero miles per gallon. Despite this, millions of UK drivers leave their engines idling every day - waiting outside school gates, sitting in a drive-thru queue, or defrosting the car on a cold morning. Each of those minutes is fuel bought and burned for nothing.
The financial cost, worked
How much fuel does an idling engine actually consume? Typical figures quoted for a 2.0-litre engine are 1.0 to 1.5 litres an hour. That sounds small until you annualise it. Ten minutes a day - five warming up, five waiting - is about 61 hours a year:
| Idle consumption | Litres a year | Petrol at 161.2p | Diesel at 182.4p |
|---|---|---|---|
| 1.0 litre/hour | 61 | £98.33 | £111.26 |
| 1.5 litres/hour | 91 | £146.69 | £165.98 |
It is also a cost with no upside at all: unlike every other fuel decision in these guides, idling buys you nothing - not distance, not convenience you could not have had by switching off, and on a cold morning not even a faster warm-up.
For context, that is the same order as the £71.50 a year a driver saves by filling up 5p a litre cheaper every week - except the idling saving requires no detour, no app and no change of forecourt. Just a switched-off key.
The ten-second rule
There is a persistent myth that starting an engine requires a surge of fuel, so leaving it running is cheaper for brief stops. That was true for carburetted cars in the 1980s. It is completely false for modern fuel-injected engines: restarting uses roughly the fuel of 10 seconds of idling. If you will be stationary longer than that, switching off and restarting saves fuel, every time.
Stop-start technology
If your car has automatic stop-start, let it work. It exists specifically to remove idling losses in traffic, and it restarts the engine more efficiently than a cold start. Some drivers disable it out of habit or worry about starter wear - the systems are designed for tens of thousands of restarts, and the fuel saving is real in the stop-start traffic where they operate.
The warm-up idle is the big one
The largest single idling habit is the morning warm-up: starting the car and leaving it running to "get some heat in" while scraping the ice off. Modern engines do not need it - they reach operating temperature faster under light load, driving gently, than they do standing still. Idling to warm up burns fuel, delays the warm-up, and leaves the engine spending longer in its coldest, most wearing state. Scrape the windows first, start the engine last, and drive off gently within a few seconds. Our winter driving guide covers the full cold-weather routine.
There is also the small matter of the law: leaving a parked car's engine running unnecessarily is an offence under road traffic rules, and councils can issue penalties for it - the school-gate idle is the textbook case.
Where idling is unavoidable
Some idling is not a choice: stationary traffic with a stop-start-less engine, or waiting in a queue you cannot leave. The fixable idling is the voluntary kind - the warm-up, the parked wait, the drive-thru. That is where the 60 to 90 litres hide.
Cheaper fuel beats better mileage
Driving technique is worth a few percent on consumption. Choosing the right forecourt is often worth more: with more than 10p a litre between the cheapest and dearest stations in most towns, a two-minute check before you set off usually saves more than a month of careful driving. Find fuel prices near me or browse prices by region.
Frequently asked questions
Does stop-start wear out the starter motor?
The components in stop-start systems are upgraded for the duty cycle. Over the life of the car, the fuel saved comfortably outweighs any marginal wear.
Is it better to idle or switch off in a drive-thru queue?
If you expect to sit more than about ten seconds, switch off. The restart costs less fuel than the wait.
What about hybrid cars?
Their computers already do the work, shutting the engine whenever it is not needed. A hybrid left in ready mode at a standstill burns almost nothing, which is the same trick the ten-second rule asks of a conventional car.
Does idling damage the engine?
Prolonged idling keeps the engine below operating temperature for longer, which is a mildly wearing state, and fuel-diluted oil over very long idle habits is a known fleet issue. The waste of fuel is the certain cost; the wear is the possible one.
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