I have a fuel card which pays for all my petrol, and have a car allowance which funds my own private car. Now, last year I did no business mileage, so I got charged 40% tax on my petrol as a cash benefit. This year, I'm travelling to bristol approx once a week, a 200 mile round trip. Now, I understand that I can claim 40p per mile for these business miles, but how do I work out how many miles a year I need to do to cover my own personal miles? I.e where do I break even? lets assume a price per litre of £1.20, and my car averages 25mpg (usually about 26.5 but lets round it down). I do around 10000 miles per year personal miles. so my cost per mile is: 25mpg / 4.546 litres per gallon = 5.5 miles per litre / £1.20 per litre = 21.p per mile? I get taxed at 40%, so I actually pay 12.6p per mile. 10000 personal miles actually cost me £1260, so thats what I want to recoup this is where it gets tricky. a round trip to bristol is 200 miles (almost exactly). I can claim 40p per mile for that, which is £80. but the petrol for the trip would cost £40ish. so am I netting £40 per trip, or is it worked out differently? At £40 per trip it'd take 31 trips to break even, which means I should take the train more often I want to balance the car travelling so I don't use too many miles and affect my PCP with a nasty penalty at the end.