Fuel, insurance, and maintenance math: adding up the running costs
After depreciation, the three costs that keep charging you are fuel, insurance, and maintenance. They're predictable enough to estimate before you buy — and different enough between cars that they can flip a buying decision. Here's how to do the math honestly, one bucket at a time.
Fuel: start with your real mileage
The single most common mistake in fuel math is using the wrong annual distance. People underestimate. Check your odometer against last year's service records, or multiply your daily commute by the days you actually drive. Then:
- Take your realistic annual kilometres (or miles).
- Divide by the car's real-world consumption — not the optimistic official rating. Owner forums and independent reviews give you the truth; official figures are tested in conditions you'll never see.
- Multiply by the fuel price you actually pay near home.
The result is your yearly fuel cost. Compare two cars by plugging each one's real-world consumption into the same formula — your distance and your fuel price stay constant, so only the car's efficiency matters. For example, say you drive 15,000 km a year. A car that uses 6 L/100 km burns 900 litres; one that uses 9 L/100 km burns 1,350. That's a 450-litre gap every year, year after year — the same fuel price, the same commute, a very different bill.
Insurance: get the quote before you buy
Insurance cost varies far more between cars than buyers expect. The same driver can get wildly different quotes for different vehicles, because insurers price based on repair costs, theft rates, safety records, and claim history for that model. The fix is simple: get an insurance quote for the exact car before you sign anything. A five-minute call or quote form can reveal that the "affordable" used car carries an expensive premium, or that the pricier new car is cheap to insure because of its safety tech. Insurance is also where your personal factors hit: your driving record, your postal code, your annual mileage, and your deductible all move the number. Re-quote periodically and compare providers — loyalty is rarely rewarded in this market.
Maintenance and repairs: budget in tiers
Maintenance splits into two kinds: the scheduled and the surprising.
Scheduled maintenance is knowable. The owner's manual lists service intervals and what's included. Call a local independent mechanic and ask what a full service, a brake job, and a set of tires costs for the model you're considering. Tires alone surprise buyers regularly — larger wheels and low-profile tires cost far more to replace than standard ones, and you replace tires several times over a car's life.
Repairs are the statistical part. No one can tell you which parts will fail on your specific car, but reliability records for the model are real data. Some models consistently cost less to keep healthy; others have known expensive failure points — transmissions, turbos, electronics — that show up again and again in owner reports. Read long-term owner reviews and reliability surveys for the specific model and generation, not the brand's reputation in general. A practical budgeting approach: set aside a monthly amount for repairs that grows as the car ages. A car under warranty needs little; a car past year six or seven needs a real line item.
Putting it together
Fuel, insurance, and maintenance together are your car's annual running cost. For example, if you estimate $1,800 for fuel, $1,200 for insurance, and $900 for maintenance and repair reserves, your car costs you $3,900 a year before depreciation — roughly $325 a month that never shows up on the dealer's worksheet. Running costs like these are why two cars with similar sticker prices can have very different total costs: the efficient, cheap-to-insure, reliable one quietly wins every single year you own it.
The honest-math rules
- Use your actual driving distance, not your optimistic one.
- Use real-world fuel consumption, not the official rating.
- Get an insurance quote for the exact car before buying.
- Price tires, brakes, and a service for that model at a local shop.
- Budget a repair reserve that increases as the car ages.