Quick answer
Annual fuel cost = miles per year ÷ mpg × price per gallon. Driving 12,000 miles at $3.50: a 20 mpg car costs $2,100 a year and a 35 mpg car $1,200, saving $900 and 257.1 gallons.
Enter yearly miles, current and new fuel economy and the fuel price. The calculator compares the two costs. Use this fuel savings calculator to check your own figures.
Related tools: Fuel Cost Calculator: Trip fuel cost from distance, fuel economy and price. Distance per Tank Calculator: Range on a full tank from tank size and fuel economy. MPG Calculator: Miles per gallon from distance and fuel used.
How to use the Fuel Savings Calculator
- Enter miles driven per year (above 0).
- Enter current fuel economy (mpg) (above 0).
- Enter new fuel economy (mpg) (above 0).
- Enter fuel price ($ per gal) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Miles driven per year | A number | > 0 |
| Current fuel economy | A number, in mpg | > 0 |
| New fuel economy | A number, in mpg | > 0 |
| Fuel price | A number, in $ per gal | > 0 |
Formula and method
Formula
annual cost = miles ÷ mpg × price
IEEE-754 double precision; shown to the decimals indicated.
Savings = current cost − new cost.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Miles driven per year = 12000; Current fuel economy = 20; New fuel economy = 35; Fuel price = 3.5.
| Result | Value |
|---|---|
| Annual savings | $900.00 |
| Annual fuel cost (current) | $2,100.00 |
| Annual fuel cost (new) | $1,200.00 |
| Gallons saved | 257.1 |
Example 2
Inputs: Miles driven per year = 15000; Current fuel economy = 25; New fuel economy = 25; Fuel price = 4.
| Result | Value |
|---|---|
| Annual savings | $0.00 |
| Annual fuel cost (current) | $2,400.00 |
| Annual fuel cost (new) | $2,400.00 |
| Gallons saved | 0 |
Example 3
Inputs: Miles driven per year = 8000; Current fuel economy = 30; New fuel economy = 50; Fuel price = 3.2.
| Result | Value |
|---|---|
| Annual savings | $341.33 |
| Annual fuel cost (current) | $853.33 |
| Annual fuel cost (new) | $512.00 |
| Gallons saved | 106.7 |
The first line is the headline result (annual savings). Below it the fuel Savings Calculator lists annual fuel cost (current), annual fuel cost (new) and gallons saved, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Diminishing returns
Gains in mpg matter less the higher it already is. Going from 20 to 35 mpg saves 257 gallons a year here, but going from 35 to 50 saves only 103 gallons (343 minus 240). Fuel use is miles divided by mpg, so the saving shrinks as mpg rises.
Using it to decide
Divide the extra cost of the more efficient car by the annual saving to estimate payback in years. Also consider insurance, maintenance and how long you will keep the car. Fuel prices change, so test a high and a low price.
How the result changes with miles driven per year
Holding every other input at the first worked example, this table changes only miles driven per year. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Miles driven per year | Annual savings | Annual fuel cost (current) | Annual fuel cost (new) |
|---|---|---|---|
| 6000 | $450.00 | $1,050.00 | $600.00 |
| 12000 | $900.00 | $2,100.00 | $1,200.00 |
| 24000 | $1,800.00 | $4,200.00 | $2,400.00 |
| 48000 | $3,600.00 | $8,400.00 | $4,800.00 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Miles driven per year: entering "0" shows "Miles driven per year must be greater than 0." beside that field and no result.
- New fuel economy: entering "0" shows "New fuel economy must be greater than 0." beside that field and no result.
Choosing between the Fuel Savings Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Fuel Cost Calculator](/automotive/fuel-cost-calculator/) | distance, fuel economy and fuel price | Trip cost |
| [Distance per Tank Calculator](/automotive/distance-per-tank-calculator/) | tank size and fuel economy | Range |
| [MPG Calculator](/automotive/mpg-calculator/) | miles driven and gallons used | Fuel economy |
| [Savings Calculator](/finance/savings-calculator/) | initial amount, annual interest rate and years | Savings balance |
| [Fuel Economy Converter](/converters/fuel-economy-converter/) | value, from and to | Miles per US gallon (mpg) → Litres per 100 km (L/100 km) |
Background: vehicle sizing and speed
A taller tyre travels farther per revolution, so the speedometer reads low and the effective gear ratio becomes numerically lower; a shorter tyre does the opposite. True speed is roughly the speedometer reading times the new tyre diameter divided by the old one. Verify with GPS over a known distance before changing parts.
Assumptions and limitations
- Prices and driving change over time
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for miles driven per year and new fuel economy to confirm this.
Frequently asked questions
Is gallons per 100 miles better than mpg?
It shows savings more directly, because fuel used is proportional to it.
Does it include electricity?
No, it assumes fuel priced per gallon.
What if I drive more?
Savings scale in proportion to miles.
What does the Fuel Savings Calculator calculate?
Yearly fuel savings from a more efficient vehicle. It returns Annual savings, Annual fuel cost (current), Annual fuel cost (new) and Gallons saved.
What formula does the Fuel Savings Calculator use?
annual cost = miles ÷ mpg × price. Savings = current cost − new cost.
What do I need to enter in the fuel Savings Calculator?
You enter Miles driven per year, Current fuel economy (mpg), New fuel economy (mpg) and Fuel price ($ per gal).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Prices and driving change over time.
What is an example of a fuel Savings result?
With miles driven per year 12000, current fuel economy 20, new fuel economy 35 and fuel price 3.5, the annual savings is $900.00.
Related calculators
- Fuel Cost Calculator — Trip fuel cost from distance, fuel economy and price.
- Distance per Tank Calculator — Range on a full tank from tank size and fuel economy.
- MPG Calculator — Miles per gallon from distance and fuel used.
- Fuel Economy Converter — Convert mpg (US and UK), km/L and L/100 km.
Sources
- OpenStax, Prealgebra 2e (Rice University): fractions, decimals, percents, ratios and rounding
- NIST Special Publication 811, Guide for the Use of the International System of Units (SI), Appendix B conversion factors (international inch 25.4 mm, avoirdupois pound 0.45359237 kg)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.