Gas Savings Calculator
How much a more fuel-efficient car saves you in gas — per year, in gallons, and over five years.
How it works
gallons = miles ÷ MPG · annual fuel = gallons × price · savings = current fuel − new fuel
Each car’s yearly fuel is your annual mileage divided by its MPG, times the pump price. The difference is what the more efficient car saves per year, and five years of that shows the payback that matters when comparing purchase prices. A key quirk: fuel savings depend on the gap in gallons used, not the gap in MPG, so a jump at the low end of the MPG scale saves much more than the same jump at the high end.
Worked example
Driving 12,000 miles a year, a 22-MPG car burns 545 gallons ($1,909 at $3.50); a 35-MPG car burns 343 gallons ($1,200). That’s about $709 saved a year — 203 gallons — and roughly $3,545 over five years.
Frequently asked questions
Why does going from 15 to 20 MPG save more than 30 to 40?
Because savings come from gallons, not MPG. Over 12,000 miles, 15→20 MPG cuts 200 gallons, while 30→40 MPG cuts only 100 — even though the second jump is a bigger number. This is the “MPG illusion,” and it’s why upgrading a gas-guzzler pays off fastest.
Should I count the higher price of the efficient car?
Yes, for the full picture. Divide any price premium of the efficient car by the annual savings to get the payback in years. If a car that saves $700 a year costs $2,100 more, it pays for the difference in three years, then saves from there.
Does an electric car change this math?
It replaces gallons with kilowatt-hours. To compare, work out the EV’s cost per mile (kWh per mile × your electricity rate) against the gas car’s cost per mile (price ÷ MPG); an EV’s per-mile energy cost is often a third or less of a gas car’s.
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This calculator is for educational purposes. Double-check important results before acting on them.