This Wiki is not meant to kill off man maths - quite the opposite actually. It shall extend the imagination for everyone wanting to know the cost of a car.

In order to get a good result, you should know how long you want to keep the car, and how much you'll be driving it. To keep it consistent, this text shall be based on mileage per year, months to be kept and cost per month.

Annotations shall be hidden by spoilers or footnotes to keep the most important points on top.


Contibuting Factors

Ownership


Deprecation


Depending on your way of financing the car, this is either
  • the price you have paid minus what you sold it for at end of ownership (requires prediction)
  • the sum of all leasing payments (and possible corrections and end of term) (leasing is a guaranteed deprecation if used as planned)
  • the sum of all finance payments including interest and balloon payments minus resale income
Divide that sum through months of ownership.
You might include loss of interest when paying with saved cash; for example compared to putting the cash towards a mortgage.

If planning to buy a car, you may compare what is best for your needs. A new Alfa might be more expensive than an equally sized/specced new Audi when leased for 20k mls pa and 36 months, but cheaper when bought used cash and driven 4k mls pa for 120 months.

Administration


One-time cost if not already included in Deprecation. Ie. plates, OTR, travel, transport, advert to sell the car privately in the end, etc.

Modifications and Add-Ons


Need an extra set of winter tyres or a ski rack? Also interesting when you want to make an upgrade to a used car, and you're comparing to another, that wouldn't need that upgrade. Also, some modifications may reduce a resale value: the add the cost of the modification to the reduction of resale value, and divide by months the vehicle will be kept.

Running Cost


Maintenance and Repairs


This includes inspection/services as well as MoT tests and replacing worn parts like wiper blades, tyres, filters, exhaust renewal, clutch, brakes, wheel bearings, etc.
Typical lifetime of a component depends on vehicle/quality and driving style.

Fuel and Oil


How much do you need to fill up? Don't rely on the figures from manufacturers - they are only meant to be used to compare new cars, as they are done in a lab under equal conditions.
Journalist road tests might give a more realistic figure; although there is a difference if you trash that S8 around the ring, or waft the same between Lyon and Marseilles.

Fixed Cost


Road Tax


Your annual road taxes divided by twelve. Also include possible tolls if you want to know the absolute cost.

Insurance


Your insurance cost over lifetime broken down to a month.
no-claims bonus might change over the years

Storage


This comes into account if it's required for a particular choice of (weekend) car, or if you're living in central London and want to know the absolute cost.

Example Calculations

Case 1: New BMW 330i


tbd
Ownership for Deprecation Administration Modifications Maintenance/Repair Fuel/Oil Tax Insurance
48m, 20k mls

Case 2: Used MX-5


Ownership for Deprecation Administration Modifications Maintenance/Repair Fuel/Oil Tax Insurance
24m, 6k mls