Gas Cost Calculator
Weekly, Monthly, Annual.
Compute weekly, monthly, and yearly fuel cost for any vehicle — gas, diesel, or EV. Run two vehicles side-by-side with a 10-year spend delta. Trip-mix slider weights city vs highway for realistic real-world cost.
What actually moves your fuel bill
Most drivers underestimate how much fuel spending scales with small efficiency differences. A 4-MPG swing on a 15,000-mile-a-year commute can mean $400-$700 per year at current prices. Here are the six levers that actually move the needle:
- Tire pressure. Under-inflated by 10 PSI costs 3-5% in fuel. Check monthly, cold.
- Air filter. A clogged intake filter cuts efficiency 5-10%. Inspect every oil change.
- Idling. 10 minutes idling = roughly 0.1-0.3 gallons. Multiply across a year.
- Highway speed. Most vehicles peak at 50-55 mph. Over 70 mph, expect 15-20% loss.
- Oxygen sensor. A failing O2 sensor runs the engine rich; MPG drop of 10-40%.
- Spark plugs. Worn plugs cause misfires that hurt MPG and throw codes.
When to take your MPG drop seriously
A 5-10% drop after a cold snap is normal — winter gas has lower energy density and engines run rich until warm. A sustained 15%+ drop is a diagnostic signal. Common culprits in order of likelihood: dirty air filter, under-inflated tires, failed thermostat (engine never warms up), O2 sensor, catalytic converter.
Frequently asked questions
How much does gas cost per mile?
Divide your local gas price by your vehicle MPG. At $3.80/gal and 28 MPG, each mile costs about $0.136. Our calculator does this per trip, per week, per month, and per year so you can see the real impact of a long commute or a gas-thirsty truck.
Does this tool support diesel and electric vehicles?
Yes — use the fuel-type toggle. Gas and diesel use miles-per-gallon plus $/gal. EVs use miles-per-kWh plus $/kWh. Most home-charged EVs land around 3 to 4 cents per mile, versus 12 to 20 cents for a typical gas car. The A/B compare lets you run any pair side-by-side with a 10-year spend delta.
Why is my actual fuel spend higher than the calculator shows?
Stop-and-go driving, cold weather, roof racks, short trips before warm-up, underinflated tires, and aggressive acceleration can each cost 5 to 15% in real-world MPG. Use your observed MPG — total miles divided by total gallons over the last three tanks — for the most accurate number.
What MPG should I use if I don't know my number?
Check the window sticker number (EPA combined) as a starting estimate. Most drivers land 5 to 10% below the EPA number because of short trips, cold starts, and city driving patterns. If you want a precise figure, fill the tank, record the odometer, drive normally for a week, refill, and divide miles by gallons added.
How much can I save by changing my driving style?
Smooth acceleration and highway cruising at 60 rather than 75 mph can save 15 to 25% on the same route. Combining short errands into one trip adds another 5 to 10% because cold starts burn the most fuel. A $300 per month fuel bill can drop by $60 to $80 with no equipment changes.
Is this a good way to compare two vehicles before buying?
Yes — use the A vs B compare. Fill in city + highway efficiency for each and the trip-mix slider weights them. The 10-year delta between a 22 MPG truck and a 38 MPG sedan at 15,000 miles/year and $3.80/gal is roughly $11,000 — often the difference between monthly payments.
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