Available exclusively for iOS, Mileage Expense Log is one of the most affordable trackers you can get. Although there’s a free version, trust me when I say you should buy the Pro version
That’s a one-time price that buys you freedom from some seriously intrusive advertising. Just as important, it enables automatic trip tracking, though the implementation here is a bit confusing.
So is the interface, which starts off with a blank summary (blank because you haven’t recorded any drives yet) and no clear indication of what you’re supposed to do. Tap the “+”, however, and you’ll see fields for recording your first trip: vehicle, destination, purpose, etc.
From here you can choose Auto Track or Odometer, the latter if you prefer to manually log your mileage. But the former includes Start and Stop buttons, which would seem to challenge the idea of automatic tracking.
Once you figure out the interface, however, MEL works well enough. It can sync your data to iCloud or Dropbox, and it’s even Apple Watch-compatible. Just take note that its export options are limited to HTML and CSV.