What does your car cost per month? Fuel use, cost per km and expenses

What goes into the cost of a car#

Most estimates come out too low because they only count fuel. Look at every expense, including the ones that come once a year:

RCA is Romania's compulsory third-party motor insurance, CASCO is optional comprehensive cover, the ITP is the periodic roadworthiness test and the rovinietă is the road-use vignette. There's one more cost you won't see on any receipt: the car loses value every year. It doesn't go into the monthly sum, but it matters when you compare the car with other ways of getting around.

How to measure fuel consumption properly: full to full#

1. Fill the tank until the pump nozzle clicks off and note the mileage on the dashboard.
2. Drive as you normally do until the next fill-up.
3. Fill up to full again, ideally at the same station and pump, and note the litres and the mileage.
4. Work it out: the litres you just put in, divided by the kilometres since the last full tank, times 100. The result is consumption in litres per 100 km.

A worked example: if you put in 40 litres after 500 km, consumption is 40 ÷ 500 × 100 = 8 l/100 km. The litres from the first fill-up don't count: they were for the driving before it.

One tank tells you little. Average over several fill-ups in a row: that evens out a more generous fill or a week of heavy traffic.

Why the dashboard figure differs from yours#

The trip computer estimates consumption from engine data and may show something different from your calculation. And real consumption changes from month to month. It usually goes up with:

• Short trips on a cold engine and driving in heavy traffic.
• Cold weather: in winter the engine takes longer to warm up.
• Air conditioning, a roof box and heavy loads.
• Low tyre pressure: check it cold, against the carmaker's label.
• Postponed maintenance: filters and oil are changed as the service book says.

Cost per kilometre: how to work it out#

The cost per km is the total spent over a period divided by the kilometres driven in the same period. Use a long period, ideally 12 months: RCA, the ITP or the rovinietă are paid in one go, and in a single month they would push the figure up or down.

• Fuel cost per km: consumption times the price per litre, divided by 100. It tells you what the driving alone costs.
• Total cost per km: includes everything, from insurance to parking. It tells you what each kilometre in your car really costs.

With the total cost per km it's easier to compare the car with other options, split the cost of a trip fairly with friends or of a car shared in the family, or see whether a second car is worth keeping.

What it costs per month and how to plan for it#

Car costs don't arrive evenly: a month with RCA, the ITP and new tyres can cost as much as several ordinary months. So:

• Look at the 12-month average, not the current month, when you want to know what the car costs.
• Set aside part of the yearly costs each month (RCA, ITP, rovinietă, car tax), so they don't all land at once.
• Log every expense straight away. Parking and car wash receipts are the easiest to lose, and they add up.

How to track your car's costs in CariX#

In the free driver account, the car's "Costs" page shows what it costs you per month and per km, and how much fuel it uses. The steps:

1. Add your car, with its fuel type.
2. "Add expense" for every payment, and pick the type: Fuel, Parking, Car wash, Tolls, RCA insurance, CASCO insurance, Repairs / service and others.
3. On fill-ups, enter the litres and the mileage too. From them CariX works out consumption in l/100 km from one fill-up to the next, and the mileage also goes into the car's km history.
4. Open "Costs": see this month and the last 12 months, the monthly average, the cost per km, the average consumption and the charts "Spending per month", "Consumption over time" and "Where the money goes".

The page is upfront about its limits: consumption appears after two fill-ups in a row with litres and mileage, and works best if you fill the tank every time; the cost per km appears once you've entered the mileage at least twice, 30 days apart; values that look wrong are left out of the average. For electric cars CariX doesn't work out consumption in litres.