E85 Break-Even Price Calculator

Start with the operating case

Find the E85 price that produces the same fuel cost per mile as gasoline — both sides of the comparison must describe the same vehicle and operating period.

The comparison excludes availability, cold-start behavior, and maintenance considerations — that condition defines when e85 break-even price is comparable with another result.

Building one consistent data set

For Gasoline price, use the quantity described as price of the gasoline grade being compared — in the vehicle record, keep the sign convention and reference plane consistent with the formula.

Gasoline fuel economy is defined here as measured or expected economy on gasoline — keeping that definition intact requires you to match the fuel quantity to the same distance, fill method, and operating period.

The E85 fuel economy entry represents measured or expected economy on E85 — before calculating, match the fuel quantity to the same distance, fill method, and operating period.

Loaded values as a demonstration

One reproducible example uses Gasoline price = $3.65/gal, Gasoline fuel economy = 27 mpg, and E85 fuel economy = 20.5 mpg.

The resulting values are E85 break-even price = $2.77/gal, Gasoline cost per mile = $0.135/mi, and E85 economy difference = -24.1%.

If your notes raise the question of how to estimate how long an efficiency improvement takes to recover its installed cost through fuel savings, move to the Fuel Economy Improvement Payback without changing this page's inputs.

The mathematical relationship

In “break-even E85 price = gasoline price × E85 MPG ÷ gasoline MPG,” e85 break-even price follows from the displayed relationship among gasoline price, gasoline fuel economy, and e85 fuel economy.

No term beyond gasoline price, gasoline fuel economy, and e85 fuel economy is introduced in “break-even E85 price = gasoline price × E85 MPG ÷ gasoline MPG.”

E85 break-even price answers “Find the E85 price that produces the same fuel cost per mile as gasoline.” The additional displays, Gasoline cost per mile and E85 economy difference, are a different view of the same entered measurements.

Use fuel economy measured on comparable routes — when that condition changes, compare separate calculator runs instead of blending the inputs.

Because the comparison excludes availability, cold-start behavior, and maintenance considerations, a disagreement between e85 break-even price and an outside reference should trigger a review of gasoline price and e85 fuel economy.

What remains a separate check

A change in gasoline price is not isolated if another vehicle condition changed between the two cases — for gasoline price, the page specifically expects price of the gasoline grade being compared.

Interpreting this calculator