Methodology
Where the numbers come from
A tool about money should say what it invented and what you told it. The short answer is that it invents almost nothing: every figure in your result is one you entered, or a zero that is listed back to you.
A blank field counts as zero, and says so
Only two inputs are required — how long you keep the car and how far you drive it. Everything you leave empty is treated as zero rather than being filled with a guess, and every field treated that way is listed in the assumptions log beside your result. So a total is never quietly inflated by a number you did not choose, and you can always see which costs are missing from it.
There is no fuel or electricity price database
Deliberately. A country's currency and whether its road signs read miles or kilometres are stable facts. A fuel price is not — it moves weekly and varies by station. Presenting an invented average as a market default would be worse than presenting nothing, because you would have no way to tell it apart from a figure you supplied. If you want energy costs in your total, you enter the price you actually pay.
The only two estimates, and both are suggestions
Two fields offer a starting figure as you type, because leaving them at zero distorts a result more than a rough estimate does. Both are pre-filled suggestions you can overwrite, and neither is used unless it ends up in the field. Nothing else in the calculation is estimated.
Suggested resale value
The suggestion assumes a car keeps about 70% of its value every three years, compounding — so roughly 70% after three years and about 49% after six. It is a broad industry rule of thumb, not a valuation of your specific car: mileage, condition, model and market all move it, and a real quote for your car will always be better. Replace it whenever you have one.
Suggested annual tyre cost
The suggestion spreads one set of tyres, taken as 600 in your chosen currency, over a life of 50,000 km (about 31,000 miles), scaled to the distance you drive each year. Both figures are mid-range, and performance or winter tyres will exceed them.
Currency and units
Currency and distance unit are chosen from your browser's region and can be changed at any time from the header. Changing them re-labels your figures — it does not convert them, because the tool holds no exchange rates. Enter every amount in the currency you selected.
How the total is put together
Costs are grouped into six categories, with hidden and opportunity costs kept separate and added on top, so the categories always reconcile to the total. Resale value is applied as a credit against what you paid rather than as a negative cost. A leased car receives no resale credit unless you exercised a purchase option, because otherwise there is nothing left to sell.
For what each cost category contains, see the features page