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.
Want the full breakdown — driving style, mechanical condition, route + timing, the new-car math? We wrote it up properly.
Read “How to cut your fuel bill without trading the car” →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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