Since April 2002 company car tax has been based on a car's list price for tax purposes (generally list price plus accessories, less capital contribution) and official C02 emission figure.
Using HM Revenue & Customs benefit rules for each year, the official CO2 figure for the car (measured in grams per kilometre (g/km)) is converted to a percentage multiplier, applied to the list price for tax purposes to determine the taxable benefit charge for the year.
Initially the percentage multiplier increased 1% for each 5g/km increase in CO2 from a minimum of 15% at 155g/km or less, up to a maximum of 35%. There was a 3% supplement for diesels up to the maximum of 35%.