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MPG Comparison Calculator
Compare annual and monthly fuel costs with separate prices for each car, plus fuel-only payback for an extra purchase cost.
Formula Each vehicle: annual miles ÷ its MPG × its fuel price. Fuel-only payback: extra purchase cost ÷ annual fuel saving.
Compare MPG, fuel prices and purchase-price payback
Use the same annual mileage for both vehicles, but enter each vehicle's own MPG and fuel price. Annual fuel cost is miles divided by MPG, multiplied by that vehicle's price per U.S. gallon. The result also shows yearly gallons and the monthly cost difference. Enter an extra purchase cost above zero to estimate how many years of fuel savings would recover it.
Worked example
At 12,000 miles and $3.50 per gallon for both cars, a 25-mpg vehicle costs $1,680 in fuel per year. A 35-mpg vehicle costs $1,200. That saves $480 per year, or $40 per month, so an extra $2,400 purchase cost takes five years to recover from fuel savings alone. If the 35-mpg car's fuel instead costs $4.50 per gallon, its annual cost rises to $1,542.86 and the saving falls to $137.14.
How to use the result
Use U.S. MPG, not Imperial MPG or electric-vehicle MPGe. Choose the fuel grade required by each vehicle's manufacturer and enter local pump prices. The payback estimate holds miles, MPG and prices constant. It excludes financing, taxes, insurance, maintenance, depreciation and resale value, so it does not establish total ownership cost or recommend buying a car. Real-world MPG and future prices can change the result.
Sources and assumptions
U.S. EIA public gasoline price table Accessed 2026-09-05Calculation methodology. Worked examples use the expressly stated inputs; sample prices are illustrative rather than local quotes.
Use a vehicle service sheet next
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Frequently asked questions
- How much money does a higher MPG save?
- Divide annual miles by each vehicle's MPG and multiply by its fuel price, then subtract the comparison cost from the current cost. Higher MPG can still cost more if the comparison vehicle's fuel is sufficiently expensive.
- Why is the saving negative?
- The comparison vehicle costs more to fuel at your inputs. It may have lower MPG, a higher price per gallon, or both. Extra purchase cost is separate from this annual fuel difference.
- Can I compare regular and premium fuel costs here?
- Yes. Enter each vehicle's price per U.S. gallon separately, using the fuel grade specified for that vehicle. The comparison does not assume that both fuels cost the same.
- How long do fuel savings take to recover a higher purchase price?
- Divide the extra purchase cost by the annual fuel saving. An extra $2,400 with $480 in annual savings takes five years at constant inputs. If annual savings are zero or negative, there is no fuel-only payback. Leave extra purchase cost at zero to skip this estimate.
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