Worked example
An official 55 MPG reduced by 15% becomes 46.8 MPG. Over 10,000 miles, that difference can materially change the annual fuel estimate.
Frequently asked questions
What percentage reduction should I use?
There is no universal figure. If you know your real MPG, use the MPG Calculator instead. Otherwise test several scenarios such as 10%, 15% and 20%.
Does winter affect MPG?
It can. Short trips, cold engines, heating demand, tyres and traffic can all influence real-world consumption.