E85 gas mileage: how much MPG do you lose?

Yes, E85 lowers your MPG. That's not a defect — it's chemistry. Ethanol contains about 27% less energy per gallon than gasoline, so a gallon of E85 simply moves you fewer miles. But "fewer MPG" and "more expensive" are not the same thing, and that's the part most people get wrong.

The real-world MPG hit

Pump "E85" is rarely 85% ethanol — it ranges 51–83% by season and region (why), so the mileage drop tracks the actual ethanol content:

• Winter E85 (~E51–E60): roughly a 15–20% MPG drop.
• Summer E85 (~E70–E83): roughly a 20–27% MPG drop.
• Blends (E30/E50): proportionally smaller — an E30 mix loses far less than straight E85.

So if your car gets 25 mpg on gas, expect ~19–21 mpg on summer E85.

Why E85 can still be cheaper — cost per mile

The number that actually matters isn't MPG, it's cost per mile. If E85 is priced 25%+ below regular, it can cost the same or less to drive despite the mileage hit. Quick example: gas at $3.50/gal and 25 mpg = $0.140/mile. E85 at $2.50/gal with a 22% MPG drop (≈19.5 mpg) = $0.128/mile — cheaper, even burning more fuel. Flip the prices and it loses. The break-even is real and worth checking every fill. (Full breakdown: is E85 actually cheaper?)

Let the app do the math

E85 App factors ethanol's energy density into a true per-mile cost and compares it to regular automatically, using each station's freshness-dated price — so you fill on E85 only when it genuinely wins.