About the MPG Comparison Calculator
This MPG comparison calculator puts two vehicles side by side and shows what each will cost you in fuel. Enter each car’s fuel economy in miles per gallon, how far you drive in a year, the price of fuel and how many years you plan to keep the car. It calculates the yearly fuel bill, the cost per mile and the total over the ownership period for both, and the difference between them.
It is useful when you are choosing between two models, deciding whether to replace an older car with a more efficient one, or checking how much a few extra MPG are really worth. Gaps in MPG matter more than they look at the low end: going from 15 to 20 mpg saves far more fuel than going from 40 to 45 mpg over the same miles, and the calculator makes that visible.
Each car can have its own fuel price, so you can compare a premium-fuel car with one that runs on regular, or a diesel with a gasoline model. Prices are held constant, and the savings ignore differences in purchase price, maintenance and insurance — combine the result with those costs for a full decision.
With the default inputs, the yearly fuel savings with the cheaper car is $596.59. Change any value above to recalculate instantly.
How to use the mpg comparison calculator
- 1Enter the combined MPG of each car (from the window sticker or fueleconomy.gov).
- 2Enter how many miles you drive per year.
- 3Enter the fuel price for each car — use the premium or diesel price where needed.
- 4Choose how many years you will keep the car.
- 5Compare the yearly and lifetime fuel costs and the savings.
Formula and method
Each car’s yearly fuel use is the miles you drive divided by its MPG, and its yearly fuel cost is that number of gallons times the fuel price you enter for it. The cost per mile is simply the fuel price divided by MPG.
The yearly saving is the difference between the two annual fuel bills, and the ownership saving multiplies it by the number of years. Because fuel use is miles divided by MPG, the savings from a given MPG improvement shrink as MPG rises — 10 mpg extra on a 20 mpg truck saves far more than 10 mpg extra on a 40 mpg hybrid.
- MPG
- Fuel economy of each vehicle, miles per US gallon
- Fuel price
- Price per gallon for that vehicle’s fuel grade
- Years
- How long you plan to keep the car
Worked examples
22 mpg SUV vs 32 mpg sedan
At 12,000 miles a year the SUV burns 545.5 gallons ($1,909.09) and the sedan 375 gallons ($1,312.50). The sedan saves $596.59 a year — about $2,983 over five years.
Pickup upgrade: 15 vs 20 mpg
Over 15,000 miles the 15 mpg truck uses 1,000 gallons and the 20 mpg truck 750. That 250-gallon difference is worth $900 a year at $3.60, or $7,200 over eight years.
Premium-fuel sports sedan vs regular-fuel hybrid
The sedan costs 15.4¢ a mile on $4.30 premium fuel, while the hybrid costs 7.1¢ on $3.40 regular. Over 10,000 miles that is $1,535.71 vs $708.33 — $827.38 a year, nearly $5,000 over six years.
Frequently asked questions
How much money does better MPG save?+
Divide your yearly miles by each MPG and multiply by the fuel price. At 12,000 miles and $3.50 a gallon, going from 25 to 35 mpg saves about $480 a year, while going from 15 to 25 mpg saves about $1,120.
Why does going from 15 to 20 mpg save more than 40 to 50 mpg?+
Fuel use is miles divided by MPG, so each extra MPG removes fewer gallons as MPG rises. Over 10,000 miles, 15→20 mpg saves 167 gallons but 40→50 mpg saves only 50 gallons. Gallons per 100 miles shows this more clearly than MPG.
Should I compare city, highway or combined MPG?+
Use the combined rating unless your driving is mostly one type. City-heavy drivers should weight the city figure, and highway commuters the highway figure. Your own logged MPG is the most accurate number for a car you already own.
Does it matter if one car needs premium fuel?+
Yes. Premium is often 60 cents to a dollar per gallon more than regular, which can wipe out a small MPG advantage. Enter each car’s required fuel price separately to compare fairly.