Fuel Savings Calculator
Thinking about a more efficient car? Enter the MPG of your current vehicle and the one you are considering, how far you drive and what you pay for fuel. You get the yearly and multi-year fuel cost difference, gallons and CO₂ saved, and how long it takes to pay back a higher price.
Last updated:
Use the EPA combined figure or your real average.
Used only for the CO₂ estimate.
Many estimates use 12,000–15,000 miles.
0 keeps today's price; e.g. 3 for 3% a year.
How to use the Fuel Savings Calculator
- Choose units: US mpg or metric L/100 km.
- Enter both vehicles: your current car as Vehicle A and the one you are considering as Vehicle B.
- Add your driving: miles or kilometers per year and the current fuel price.
- Optionally set a yearly price change and the extra cost of Vehicle B to see the payback time.
- Press Calculate savings and read the yearly difference, the multi-year total and the year-by-year table.
The fuel savings formula
Fuel used in a year is distance ÷ fuel economy (US) or distance × L/100 km ÷ 100 (metric). The yearly fuel cost is fuel used × price, and the savings are simply the cost of Vehicle A minus the cost of Vehicle B:
savings per year = (miles ÷ MPGA − miles ÷ MPGB) × price per gallon
With a yearly price change of g%, year n uses price × (1 + g)n−1, and the multi-year total adds the years together.
Yearly savings per 12,000 miles at $3.50 a gallon
Each cell shows how much less fuel money the higher-MPG vehicle needs per year. Notice how much larger the savings are when upgrading from a low-MPG vehicle.
| From → to | Gallons saved | Saved per year | Saved over 5 years |
|---|---|---|---|
| 15 → 20 mpg | 200 | $700 | $3,500 |
| 20 → 30 mpg | 200 | $700 | $3,500 |
| 20 → 45 mpg | 333 | $1,167 | $5,833 |
| 25 → 35 mpg | 137 | $480 | $2,400 |
| 30 → 40 mpg | 100 | $350 | $1,750 |
| 40 → 50 mpg | 60 | $210 | $1,050 |
Tips for a fair comparison
- Compare like with like: use EPA combined ratings for both, or your real averages for both.
- Fuel is only part of the cost: purchase price, financing, insurance, maintenance and depreciation often matter more. Use the payback field to see whether a higher price makes sense.
- Driving more makes efficiency pay faster: savings scale directly with miles driven, so high-mileage commuters benefit most.
- Premium fuel: if one vehicle requires premium, compare at its price by running the calculator twice or averaging the price difference.
Frequently asked questions
How do you calculate fuel savings between two cars?
Divide your annual miles by each vehicle's MPG to get the gallons each would use, multiply by the fuel price, and subtract. For 12,000 miles at $3.50 a gallon, a 22 mpg car uses about 545 gallons ($1,909) and a 35 mpg car about 343 gallons ($1,200), a difference of about $709 a year.
Why does going from 15 to 20 mpg save more than going from 30 to 40 mpg?
Fuel used is distance divided by MPG, so gains at low MPG remove far more gallons. Over 10,000 miles, 15 to 20 mpg saves about 167 gallons, while 30 to 40 mpg saves only about 83 gallons. This is often called the MPG illusion, and it is why L/100 km is a more linear measure.
What MPG figure should I use?
Use the EPA combined rating for a fair comparison, or your own measured average if you know it. Real-world mileage depends on speed, climate, load and driving style, so the result is an estimate.
How is the payback period calculated?
If the more efficient vehicle costs more, the calculator adds up each year's fuel savings until they equal the price difference. It does not include financing, insurance, maintenance or resale value, which can also differ between vehicles.
How much CO₂ does a gallon of gasoline produce?
According to the US EPA, burning one gallon of gasoline produces about 8,887 grams (8.9 kg or 19.6 lb) of CO₂, and a gallon of diesel about 10,180 grams. A liter of gasoline produces about 2.35 kg.
How many miles does the average American drive per year?
Estimates from the Federal Highway Administration put the average at roughly 13,000 to 14,000 miles per licensed driver, and many cost estimates use 12,000 to 15,000 miles. Use your own odometer readings for the most accurate result.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.