Ask any E85 driver what they save and you will hear a guess: "like thirty cents a gallon?" The honest answer is that savings swing with the spread between E85 and regular in your town, with your blend, and with the season — which is exactly why a guess is worthless and a running total is powerful.
The math per fill is simple
Savings on a straight E85 fill are just gallons × (regular price − what you paid). Fill 12 gallons at $2.49 while regular sits at $3.19 and you kept $8.40 in your pocket on that stop. Do that weekly and it is $400+ a year — before counting the octane you got for free.
The catch: nobody remembers what regular cost on the day they filled six weeks ago. The math is only real if it is captured at the pump.
The app now keeps the score for you
E85 App added a fill-up log: tap Log Fill on any station, and the E85 price is already filled in from the live map — you type the gallons and go. Every fill lands in a lifetime savings total that survives reinstalls, shows on your build card, and quietly keeps the community's price for that station fresh.
Got directions to a station in the app? When you come back later it asks one question — "fill up here?" — so the log builds itself.
Why tracked savings beat estimated savings
- They survive arguments. "I have saved $412 since March" ends the E85-isn't-worth-it debate in one sentence.
- They catch the bad weeks. When the spread narrows below ~20–25%, E85 can cost more per mile. A tracked total shows negative fills honestly — so you know when to skip a station, not just when to brag.
- They compound with the blend calculator. Logged fills and the mix calculator together show cost per tank AND per blend, so you can chase the cheapest E% that still hits your target octane.
What counts as a good spread
Rule of thumb: E85 needs to be roughly 20–25% cheaper than regular to win on cost per mile (ethanol carries less energy per gallon). Our live price index tracks the national and state-by-state spread daily, computed only from prices confirmed in the last two weeks — no stale carry-forward.