- What it is
- An iPhone app for plug-in hybrid owners. You log your fill-ups, and it estimates how many of your miles were electric and how many were on the gas engine. It works for regular hybrids too, just without the electric split.
- Why I made it
- My dad keeps a paper logbook for his plug-in hybrid to work out how many miles are on the gas engine, because the car doesn't really tell you. I wanted to turn his notebook into an app.
- What I did
- I designed and built it in Swift and SwiftUI, using AI as a coding tool. Everything stays on your phone, with no account and no server, and my dad tested every build.
- How it turned out
- It's been live on the App Store since October 2026, with a free version and Engine Miles Pro. Now I'm working on getting it in front of more plug-in hybrid owners.
The details
Why I built it
My dad bought a 2022 RAV4 Prime, which is a plug-in hybrid. Since the day he got it, he's kept a paper logbook to work out how many of his miles were electric and how many were on the gas engine, because the car doesn't really tell you. The odometer counts every mile, but a lot of those miles never touch the engine, and that matters for things like oil changes.
So I wanted to turn his notebook into an app. Something quick enough to use at the pump, that does the math for you.
How it works
Every time you fill up, you type in the gallons, and the app multiplies them by your car's gas-only MPG. That's an estimate of how far the engine went on that tank, and adding up the tanks gives you engine miles. It's an estimate, not a reading from the car. There's no car connection at all, and your owner's manual still has the final say on maintenance.
The oil change tracker counts down on those engine miles instead of the odometer. Once a month the app also asks you for an odometer check-in, which keeps the estimate on track.
Building it with my dad
I built it in Swift and SwiftUI, and everything stays on your phone. There's no account and no server, so your log never leaves your iPhone. The free version covers one car, unlimited fill-ups, the estimate, the oil countdown and the monthly check-in. Pro adds insights, reminders and more cars for $1.99 a month, $9.99 a year or $29.99 once.
My dad tested every build on TestFlight before it went out, and he's a great tester because he says exactly what he thinks. One screen used to say "whole car", and he asked what that was even supposed to mean, so now it says "car's lifetime".
Fill-ups and month-end check-ins, by month. 
Insights, part of Pro.
Where it's at
Engine Miles went live on the App Store in October 2026. It's still early, so right now I'm mostly working on getting it in front of more plug-in hybrid owners. There's a lot more I want to add, and my dad keeps finding things for the list.