Flex Fuel Use Calculator
Analyze your potential savings by comparing E85 Flex Fuel against regular gasoline for your vehicle.
The total distance you drive in one year.
Your vehicle’s average fuel economy when using regular gasoline.
Your vehicle’s average fuel economy on E85 (typically 20-30% lower than gasoline).
The current local price for one gallon of regular gasoline.
The current local price for one gallon of E85 flex fuel.
Calculation Results
Annual Fuel Cost Comparison
Visual representation of total annual spending on each fuel type.
Break-Even Price Analysis
| Metric | Value | Description |
|---|---|---|
| E85 MPG vs. Gas MPG | – | The fuel efficiency of E85 relative to regular gasoline. |
| E85 Break-Even Price (per gal) | – | To save money, the E85 price must be lower than this value. |
What is a Flex Fuel Use Calculator?
A flex fuel use calculator is a specialized financial tool designed to help owners of Flex Fuel Vehicles (FFVs) make an informed decision at the pump. It determines whether using E85 (a blend of up to 85% ethanol and 15% gasoline) is more cost-effective than using traditional gasoline. While the price per gallon of E85 is often lower, vehicles typically experience a reduction in fuel economy (miles per gallon) when running on it. This calculator weighs the lower price against the reduced efficiency to reveal the true cost per mile and your potential annual savings or losses. Anyone who owns an FFV and has access to both fuel types can use this tool to optimize their fuel spending.
Flex Fuel Savings Formula and Explanation
The core logic of the calculator revolves around comparing the cost per unit of distance for each fuel type. The formulas are as follows:
- Cost per Mile (Gasoline) = Price per Gallon (Gasoline) / Miles per Gallon (Gasoline)
- Cost per Mile (E85) = Price per Gallon (E85) / Miles per Gallon (E85)
- Annual Cost = Cost per Mile * Annual Miles Driven
- Total Annual Savings = Annual Cost (Gasoline) – Annual Cost (E85)
A positive result for Total Annual Savings indicates that using E85 is cheaper over the course of a year, while a negative result means gasoline is the more economical choice. Our E85 vs gasoline calculator performs these calculations instantly.
Variables Explained
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| Annual Distance | Total distance driven in a year. | Miles or Kilometers | 5,000 – 30,000 |
| Gasoline Fuel Efficiency | Vehicle’s rated MPG or L/100km with gasoline. | MPG or L/100km | 15 – 50 MPG |
| E85 Fuel Efficiency | Vehicle’s rated MPG or L/100km with E85 fuel. | MPG or L/100km | 10 – 40 MPG |
| Gasoline Price | The cost of one unit (gallon or liter) of gasoline. | Currency per Gallon/Liter | $2.50 – $6.00 / gal |
| E85 Price | The cost of one unit (gallon or liter) of E85 fuel. | Currency per Gallon/Liter | $2.00 – $5.50 / gal |
Practical Examples
Example 1: Clear Savings with E85
Imagine a scenario where the price gap between gasoline and E85 is significant.
- Inputs:
- Annual Distance: 15,000 miles
- Gasoline MPG: 22
- E85 MPG: 17
- Gasoline Price: $4.00/gallon
- E85 Price: $3.00/gallon
- Results:
- Annual Gasoline Cost: (15,000 / 22) * $4.00 = $2,727
- Annual E85 Cost: (15,000 / 17) * $3.00 = $2,647
- Annual Savings: $80
In this case, despite the lower MPG, the substantially lower price of E85 leads to annual savings. Find out if E85 is worth it for you with our fuel efficiency calculator.
Example 2: Gasoline is More Economical
Here, the price of E85 is not low enough to offset the efficiency loss.
- Inputs:
- Annual Distance: 12,000 miles
- Gasoline MPG: 30
- E85 MPG: 23
- Gasoline Price: $3.50/gallon
- E85 Price: $3.10/gallon
- Results:
- Annual Gasoline Cost: (12,000 / 30) * $3.50 = $1,400
- Annual E85 Cost: (12,000 / 23) * $3.10 = $1,617
- Annual Loss: -$217
This demonstrates a common situation where using E85 would actually cost more over the year. A detailed gas mileage calculator can help you track your own vehicle’s performance.
How to Use This Flex Fuel Use Calculator
- Select Unit System: Choose between ‘US (Miles, Gallons)’ and ‘Metric (Kilometers, Liters)’. The labels will update automatically.
- Enter Annual Distance: Input the total distance you typically drive per year.
- Enter Fuel Efficiencies: Provide your vehicle’s average MPG (or L/100km) for both regular gasoline and E85. You can find this in your vehicle’s manual or through real-world testing.
- Enter Fuel Prices: Input the current local prices for one gallon (or liter) of both fuel types.
- Analyze the Results: The calculator instantly updates. The primary result shows your net annual savings. A positive number means E85 saves you money. Intermediate results show the cost per mile and total annual cost for each fuel, giving you a complete picture of your flex fuel savings.
- Check the Break-Even Chart: The chart and table visualize the cost comparison, making it easy to see which fuel is the better financial choice.
Key Factors That Affect Flex Fuel Savings
- Price Spread: The difference in price between gasoline and E85 is the most critical factor. A wider gap in favor of E85 is needed to offset the MPG loss.
- MPG Reduction Percentage: The energy content of E85 is lower, causing an unavoidable drop in MPG. This drop can vary from 15% to over 30% depending on the vehicle. Knowing your specific vehicle’s reduction is key to an accurate fuel cost comparison.
- Annual Mileage: The more you drive, the more any potential savings (or losses) are amplified. High-mileage drivers benefit most from choosing the correct fuel.
- Ethanol Content: The actual ethanol content in “E85” can legally vary by season and region (from 51% to 83%). Lower ethanol content will lessen the MPG penalty but might come at a higher price.
- Driving Habits: Aggressive driving with rapid acceleration tends to decrease fuel economy more significantly with E85 than with gasoline.
- Fuel Availability: The convenience and availability of E85 stations in your area can be a deciding factor, as going out of your way to find it can negate price savings.
Frequently Asked Questions (FAQ)
1. Why is fuel economy lower with E85?
Ethanol has about 25-30% less energy content by volume than gasoline. Since E85 is mostly ethanol, a vehicle’s engine must burn more fuel to produce the same amount of power, resulting in lower miles per gallon.
2. Can I use E85 in any car?
No. You must only use E85 in a vehicle specifically designated as a Flex Fuel Vehicle (FFV). These vehicles have modified fuel systems to handle the corrosive nature of ethanol. Using E85 in a non-FFV can cause serious engine and fuel line damage.
3. How do I know if I have a Flex Fuel Vehicle?
Check for a yellow gas cap, a badge on the vehicle (e.g., “FlexFuel,” “FFV,” or “E85”), or consult your owner’s manual. Our guide on the best flex fuel vehicles has more info.
4. How much cheaper does E85 need to be to save money?
As a rule of thumb, the price of E85 needs to be roughly equal to your vehicle’s MPG reduction percentage. For example, if your MPG drops by 25% on E85, the price of E85 needs to be at least 25% cheaper than gasoline to break even. This flex fuel use calculator determines the exact break-even point for you.
5. Does using the metric system change the outcome?
No. The calculator converts all inputs to a consistent internal standard for calculation. Whether you use miles/gallons or kilometers/liters, the final savings outcome and cost-effectiveness conclusion will be the same.
6. Is the “ethanol content” always 85% in E85?
No, the name is slightly misleading. In the US, E85 must contain between 51% and 83% ethanol, depending on the season and location, to ensure proper vehicle starting in colder weather. Our calculations use the typical efficiency loss associated with this blend.
7. Will the calculator’s “default” MPG loss apply to my car?
The default values are based on averages. For the most accurate results, you should determine your own car’s actual MPG on both gasoline and E85 by tracking your fuel consumption over a few tankfuls. Our trip fuel cost calculator can help with this.
8. Does E85 offer any performance benefits?
Yes, E85 has a significantly higher octane rating (around 100-105) than premium gasoline (91-93). In high-performance or tuned engines, this can allow for more aggressive tuning to produce more horsepower and torque. For a standard FFV, however, there is typically no noticeable performance gain.