What these apps have in common
All five apps do the same basic thing: store a list of fill-ups (date, odometer, gallons, price), calculate per-fill-up MPG, and plot the trend over time. None of them reads your car's computer for fuel data without extra hardware. All of them do roughly the same math the calculator does, just stored over time.
The differences are in the surrounding features: maintenance tracking, price comparison, multi-vehicle support, OBD-II integration, export, and the price. The table below is a quick reference; the sections after go into each app in more detail.
Quick reference
| App | Cost (2026) | Multi-vehicle | Maintenance tracking | OBD-II option | Export |
|---|---|---|---|---|---|
| Fuelio | Free, Pro ~$4 one-time | Yes | Yes (Pro) | Yes (Pro) | CSV |
| GasBuddy | Free, paid tier | Yes | No | No | Limited |
| Fuelly | Free | Yes | No | No | CSV |
| Road Trip MPG | ~$3 one-time | Yes | No | No | CSV |
| aCar | Free, Pro ~$5 | Yes | Yes | No | CSV |
Pricing and features change; check each app's site before deciding.
Fuelio
Fuelio is the closest to a "complete vehicle management" app: fill-up logging, multi-vehicle support, maintenance tracking, fuel-price tracking, cost analysis, and (with the Pro upgrade) OBD-II dongle support. The free version covers what most individual drivers need; the Pro version (around $4 one-time in 2026) unlocks the OBD-II integration and a few advanced chart types.
Where it fits: drivers who want one app to track everything about one or more vehicles, including the non-fuel maintenance and the cost side. The OBD-II option is a real feature for the right use case; the dongle cost ($15 to $50) is on top of the Pro upgrade.
GasBuddy
GasBuddy is best known as a price-comparison and station-finder app; the fuel-tracking feature is a secondary add-on. The price data is the strongest part: live prices by station, route-based price optimization, and historical price trends. The fill-up logging is basic compared to Fuelio or aCar.
Where it fits: drivers whose main interest is finding the cheapest gas near them, with the side benefit of having a log of what they paid. The paid tier (~$10/month in 2026) adds the route-optimization and some savings programs. For pure fuel-efficiency tracking, GasBuddy is not the right tool.
Fuelly
Fuelly is the community-benchmarking option. The fill-up log is straightforward, and the unique feature is comparing your MPG against the Fuelly database of similar vehicles. The comparison is a real check on whether your car is performing in line with the population, but it depends on the community's data quality.
Where it fits: drivers who want to know if their MPG is in the normal range for their vehicle, and who don't mind contributing to a community dataset. Free, web + mobile, export to CSV.
Road Trip MPG
Road Trip MPG is the simplest of the five: fill-up logging, per-trip MPG, basic charts, no maintenance tracking, no OBD-II, no community. The one-time $3 cost in 2026 is the lowest of the paid options, and the interface is the cleanest. It does the fill-up method and nothing else.
Where it fits: drivers who want a fill-up log without a lot of extra features, and who would rather pay $3 once than $5/month forever.
aCar
aCar is the "track everything about my car" option, similar to Fuelio but with a different feature balance. Fill-up logging, multi-vehicle, maintenance tracking, cost analysis, expenses, reminders, and reporting. The Pro upgrade (~$5 one-time in 2026) adds charts and cloud sync. The free version is the most usable free option of the five.
Where it fits: drivers who want the most features without the recurring subscription. aCar and Fuelio overlap heavily; the choice between them comes down to interface preference and which maintenance-tracking fields matter to you.
When the calculator is enough
For drivers who want MPG and nothing else, the homepage calculator covers the use case without an account, an app install, or a subscription. The calculator does the math and keeps no data; an app stores your history and adds the trend chart, the maintenance tracking, and (sometimes) the OBD-II integration.
If you are deciding between installing an app and just using the calculator, the right test is whether you actually look at the trend chart after the second or third fill-up. If yes, install the app. If the trend chart is something you would check once and then ignore, the calculator is the simpler answer.
When the app is the wrong tool
None of the five apps replaces a controlled fuel-economy test for regulatory or warranty purposes. The app's MPG is a fill-up-to-fill-up estimate; for an authoritative figure that a manufacturer, insurer, or regulator will accept, you need a controlled dynamometer or coast-down test from a credentialed professional. The accuracy guide covers when the fill-up method is enough and when it isn't.