Maryland fuel cost calculator

What the calculator works out

Three numbers from three inputs, and one optional comparison.

Divide your annual miles by your miles per gallon and you have gallons. Multiply gallons by the pump price and you have the annual bill. Divide that by the miles and you have a cost a mile, which is the figure worth carrying in your head, because it turns any trip into money without further arithmetic.

The fourth field is optional. Enter the economy of a car you are considering and the tool prices the same mileage in that car, then shows the difference over one year and over five.

The worked example at the default inputs

The tool opens on 12,000 miles a year, 28 miles per gallon, $3.30 a gallon, and a comparison car at 40 miles per gallon.

That is 429 gallons and $1,414 a year, which is $118 a month and $0.12 a mile. The 40 mile per gallon car burns 300 gallons over the same distance and costs $990, so it saves about $424 a year, or $2,121 across five years.

Two of those rows are things you cannot control. Two of them are decisions. The one you can act on fastest is the mileage, which is why the commute cost calculator usually finds more money than the pump does.

Where does your real MPG come from?

From your own trip computer or your own arithmetic, not from the window sticker.

The EPA figure is measured on a standard test cycle, and it exists so two cars can be compared on the same basis. It is not a promise about your commute. Real world economy is usually lower, and much lower for short cold trips, heavy stop-start traffic, roof boxes, towing, high speeds and under-inflated tyres.

Getting your own figure takes two fill-ups. Fill the tank, reset the trip meter, drive normally, fill again, and divide the miles shown by the gallons the second fill took. Do that twice across different weeks and average them. That number, not the sticker, belongs in the field.

fueleconomy.gov, run jointly by the Department of Energy and the EPA, publishes both the official ratings and economy reported by drivers of the same models. Comparing the two for your car tells you roughly how large the gap is before you have measured anything yourself.

The comparison field, and what it does not prove

It proves that one car burns less fuel than another. It does not prove that switching saves money.

A more efficient car saves fuel. Whether it saves money depends on three things this tool cannot see: what the two cars cost to buy, what they cost to insure, and what they are worth when you sell. The default comparison saves $424 a year. If the thriftier car costs $3,000 more and gives that back at resale, the switch is close to free and the saving is real. If it costs $6,000 more and depreciates faster, five years of fuel saving does not cover the difference.

So treat the saving here as one line to carry into a full comparison rather than as the answer. The true cost of ownership calculator holds the other five lines, and it is the tool that settles the question.

There is a second, quieter limit. Fuel saving scales with distance. A household driving 6,000 miles a year halves every figure on this page, and at that distance the difference between two cars is rarely worth paying for. A household driving 25,000 miles a year should probably let economy drive the choice.

A second example: the same car, a dollar more a gallon

Keep everything and change the price from $3.30 to $4.30.

The annual bill goes from $1,414 to $1,843, up $429, and the cost a mile goes from about $0.12 to $0.15. Nothing about the car or your driving changed. That is the point: the input that moves this number most is the one nobody controls, and it moves by more than a dollar a gallon between states and between years.

Prices also vary by grade and by region within the same week. Retail gasoline and diesel prices are published weekly by the Energy Information Administration by region and grade, and using a current figure for where you actually buy is more accurate than any national average. Differences of that kind are the same effect the cost of living pages track across other household spending.

If you want an honest range rather than a point estimate, run the tool twice: once at the cheapest price you have paid in the last year and once at the dearest. The answer sits somewhere in that band and no calculator can narrow it further.

What actually moves the number, ranked

On the default inputs, in order of the dollars each is worth over a year:

1. Annual mileage. Going from 12,000 to 20,000 miles adds $943. Nothing else here moves the figure that far.
2. Fuel price. A dollar a gallon is worth $429 at 12,000 miles.
3. The car. Twenty-eight to forty miles per gallon is worth $424.
4. Your own economy against the sticker. Twenty-eight down to a realistic 24 costs $236, and that gap is purely a measurement question.
5. Driving habits. Speed, tyre pressure and roof racks are real but small at this mileage, and they are the only ones you can change today.

That order is specific to 12,000 miles. Double the distance and every line doubles with it, which is why the ranking never changes but the stakes do.

Common mistakes with fuel arithmetic

• Using the window sticker. It is a test figure, not a measurement of your driving. Entering 28 when the car returns 24 understates the year by $236.
• Pricing a switch on fuel alone. The saving has to clear the difference in purchase price, insurance and depreciation before it is money rather than gallons.
• Comparing cars on gallons instead of dollars. Going from 15 to 20 miles per gallon saves far more fuel over the same distance than going from 40 to 50, even though the second sounds like the bigger jump.
• Using a national average price. Prices differ by more than a dollar a gallon between states. Use what you actually pay.
• Forgetting that the saving is capped by mileage. At 6,000 miles a year the default comparison saves about $212, which is not a reason to change cars.
• Assuming premium fuel is required. It is required only where the manufacturer says so. Where it is merely recommended, the price difference is a real cost with an uncertain return.

What this calculator does not cover

• Anything but fuel. Insurance, maintenance, tyres, depreciation and finance are absent. This is one line of a car budget, and not the largest one.
• Electric vehicles. The tool works in gallons at a pump price. Charging is billed per kilowatt hour, and the mix of home and public charging changes the answer enough that it needs its own arithmetic.
• Hybrids in mixed use. A single miles per gallon figure hides how much of the driving was electric or urban, so measure across a normal month rather than a good week.
• Price changes across the year. One price is applied to all twelve months. Fuel is seasonal and regional, so the annual figure is a snapshot, not a forecast.
• Business mileage relief. If some of these miles are deductible, the standard mileage rate published by the IRS is a separate calculation covering fuel and much else besides. This tool is not that calculation.
• Fuel taxes by state. They sit inside the pump price you enter and differ substantially. Our state pages cover the wider picture.

What should you check before switching cars?

• Measure your own economy across two full tanks rather than trusting the sticker
• Use the price at the station you actually use, not a national average
• Check real annual mileage against the odometer, not against an estimate
• Price the comparison car for insurance before assuming the saving is net
• Put the fuel saving into the full ownership calculator alongside depreciation
• Check tyre pressures and remove roof racks before blaming the car
• Look up the same model in the driver-reported economy database, not only the official rating

Fuel is the most visible car cost and rarely the biggest one. The point of getting it right is not the pump. It is that a correct cost a mile turns every other transport decision, including whether to drive at all, into arithmetic instead of instinct.

Nothing here is advice about which vehicle to buy. See the disclaimer.