What is gas actually costing you?

How this calculator works

The tool takes three inputs — how many miles you drive in a typical week, the miles per gallon your vehicle actually gets, and the price you're paying per gallon — and multiplies them out into a monthly and yearly fuel cost, plus a cost per mile. It assumes your weekly mileage and MPG stay constant, which is a simplification: real driving varies week to week with traffic, trip length and season.

The MPG figure matters more than people expect. A car's window sticker MPG is measured under controlled conditions that don't match daily driving, especially in this region. Loaded freeways, long uphill grades, and running the air conditioner through most of the year all pull real MPG down. Use your own trip-computer average or a recent fill-up calculation instead of the sticker number whenever you can.

The output is fuel cost only. It does not include maintenance, insurance, registration, depreciation, or financing — those are separate line items in the total cost of owning a car. It also doesn't adjust for the price of gas changing over the year, since it uses whatever price you enter as a single snapshot.

Using the result to decide something

• Run the same commute through two different vehicles' MPG figures side by side before you buy — the monthly gap is often bigger than people guess.
• Compare your result against your actual bank or card statement for fuel. A large gap usually means your real MPG is lower than what you entered.
• If you're weighing a longer commute for a cheaper house or a better job, multiply the added miles by your cost-per-mile figure to see the true monthly trade-off.
• Re-run the numbers whenever gas prices move meaningfully — a commute budget built on an old price gets stale fast.
• Use the annual figure, not the monthly one, when comparing fuel cost against a car's price difference — it's the number that actually shows up over a few years of ownership.

Inland Empire and High Desert driving

Commutes out of Fontana, Ontario, Rancho Cucamonga, Riverside and San Bernardino routinely run 60 to 90 minutes each way when traffic is heavy, and drivers coming down from Victorville, Hesperia and Apple Valley add the Cajon Pass grade on I-15 to that mix. Climbing and descending a mountain pass at highway speed burns noticeably more fuel than flat freeway miles, and towing or running a full load through the pass makes that worse. Summer heat across the region also means the air conditioner runs for months at a time, and idling on a congested freeway in that heat is one of the least efficient ways to burn gas. Dust and grit common to the High Desert can also clog an air filter faster than average, which quietly reduces MPG until it's replaced.

Fuel cost questions we get most

Does this account for elevation and climate?

No. The calculator uses the mileage and MPG figures you enter as flat averages. Grades like the Cajon Pass on I-15, headwinds through the Inland Empire, and running the A/C hard in summer heat all pull real-world MPG below a car's rated number, so treat the result as a floor, not a ceiling.

Should I use city or highway MPG?

Use the number closest to how you actually drive. Someone commuting from Fontana or Rancho Cucamonga into the basin on the freeway should lean toward highway MPG; stop-and-go trips around Ontario or San Bernardino surface streets should lean toward city MPG.

Why is my real fuel bill higher than this estimate?

This tool doesn't know about idling in traffic, running a roof rack, towing, worn tires, or a dirty air filter. Any of those lower MPG without changing the numbers you typed in.

Does the result include maintenance or depreciation?

No. This is fuel only. For the wear a trip adds to the car, use the road trip cost tool. For the full monthly cost of owning the vehicle, see the ownership cost guide.