Motorists are now spending an average of £5,500 a year keeping their vehicle on the road.
Depreciation in value was the biggest factor, accounting for a loss of £2,420 on average this year, a 22% increase on £1,987 last year.
Nearly all other bills paid by the driver, such as maintenance, insurance and tax have also risen, it found.
RAC spokesman Sean Morris, who compiled the cost index, said: "The second biggest investment we make after home ownership - car buying - is getting bigger.
"For such an important decision, too few of us understand the spread of costs associated with owning and running a car.
"The index results will be unwelcome news for many, but motorists must better understand the true cost of their vehicles."
The research, which the RAC compiles annually, includes the costs of loans to buy a new car, which some motorists would not pay.
The figures also include the cost for RAC membership, when there are several breakdown organisations.