Swapping the car for a bike on the commute saves money and carbon — but how much? This calculator turns your own commute into a yearly figure: the fuel you’d burn driving it, what that costs at today’s pump prices, and the CO2 it puts into the air. Cycling the same miles costs next to nothing and emits nothing, so the driving figure is, near enough, what you save.
Commute cost & CO2 calculator
Enter your one-way distance, how often you ride and a few details about the car you’d otherwise drive. Every default is editable — the fuel price especially, since it moves every week.
46 leaves room for holidays and the odd day off. Change it to suit.
UK cars average roughly 36 mpg on petrol and 43 on diesel in real driving. Set yours.
GOV.UK weekly average, mid-June 2026: petrol ~155.5p, diesel ~176.7p. Check the pump.
How the numbers are worked out
Your annual mileage is the one-way distance doubled for the return trip, multiplied by the days you commute and the weeks you do it. From there:
- Fuel used comes from your car’s mpg. UK mpg is measured in miles per imperial gallon (4.546 litres), which the calculator accounts for.
- Cost multiplies the litres by the pump price. The defaults are the GOV.UK weekly averages for mid-June 2026 — about 155.5p a litre for petrol and 176.7p for diesel — but put in what you actually pay.
- CO2 uses the UK government’s 2025 conversion factors: 2.069 kg of CO2 for every litre of petrol burned, 2.571 kg for diesel. Diesel emits more per litre, though diesel engines tend to go further on it.
It is a fuel-versus-nothing comparison, so it deliberately leaves out the costs you would carry either way — the car you already own, its tax, insurance and servicing, and the bike’s own upkeep. For the tax side of switching, our Cycle to Work Scheme guide explains how to get a bike through salary sacrifice, and if you are starting in the colder months, cycling through a British winter covers the kit and safety basics.
Frequently asked questions
Does cycling really cost nothing to run?
Not quite nothing — tyres, a chain, brake pads and the odd repair add up over a year. But it is a tiny fraction of fuelling a car, which is why the calculator treats the bike’s running cost as negligible against the driving figure.
Why use fuel cost rather than the full cost of driving?
Fuel is the cost that genuinely disappears when you leave the car at home. Tax, insurance, depreciation and servicing largely continue whether you drive to work or not, so counting them would overstate the saving. If you could give up the car altogether, the saving would be far larger.
Where do the CO2 figures come from?
They are the UK government’s (DESNZ/DEFRA) 2025 greenhouse gas conversion factors for burning road fuel. They cover the carbon released when the fuel is burned, not the full lifecycle of extracting and refining it, so the real climate figure is a little higher.
What if I would take the train or bus instead of driving?
This tool only compares cycling with driving. Public transport fares vary far too much by route and season ticket to give an honest default, so for now the comparison is car-only.
