How to Keep a Fuel Log
Written by Muneeb Rana · Last updated 21 October 2026
Quick answer: To keep a fuel log, record at every fill-up the date, odometer reading, amount of fuel, price per unit, total cost, whether you filled to full, and the station. Two full fill-ups give your real MPG or L/100km, and a month of entries shows fuel cost per mile. An app makes it a quick habit.
TL;DR
- Log date, odometer, fuel amount, price, total, full or partial.
- Two full fill-ups give your real economy.
- Monthly totals show cost per mile.
Learning how to keep a fuel log is the simplest way to understand what your car really costs. It also flags mechanical problems: a sudden drop in economy is often the first sign something's wrong.
What to record
| Field | Why |
|---|---|
| Date | Spending by month |
| Odometer | Distance between fill-ups |
| Fuel amount (gal/L) | Economy calculation |
| Price per unit | Price tracking |
| Total cost | Budget |
| Full or partial | Only full-to-full gives accurate economy |
| Fuel type and station | Compare grades and stations |
| Notes | Road trip, towing, winter |
What the numbers tell you
- Real economy: miles ÷ gallons between full fills (how to calculate MPG, MPG calculator).
- Fuel cost per mile: total fuel cost ÷ miles.
- Trends: seasonal dips are normal; sudden drops aren't.
- Budget: monthly fuel spend for planning (fuel cost calculator).
Paper, spreadsheet or app
A notebook in the glovebox works if you're disciplined. A spreadsheet is good for analysis. An app is easiest because you log at the pump. CarO's fuel log records cost, odometer, fuel type and favourite stations in litres or gallons and kilometres or miles, calculates MPG, estimates the next refuel, and shows a refueling report per car. Electricity is a fuel type, so EV charging goes in the same log. For other options see best fuel log apps.
Use it with your other records
Fuel is usually the biggest running cost you see. Combine it with services and other expenses (how to track car expenses) for the full picture, and use it to improve fuel economy.
Download CarO free on the App Store or Google Play. Free with ads; optional in-app purchases.
Sources
- FuelEconomy.gov: Find and Compare Cars: www.fueleconomy.gov (accessed 21 October 2026)
- FuelEconomy.gov: Driving More Efficiently: www.fueleconomy.gov (accessed 21 October 2026)
- AAA: Gas Prices: gasprices.aaa.com (accessed 21 October 2026)
Disclaimer: CarO and this website give general car-care information, not professional advice. Maintenance intervals and specifications vary by vehicle, so always follow your owner's manual and a qualified mechanic. Mileage and cost figures are estimates; check local tax rules before using any log for deductions.
FAQ
What is a fuel log?
A record of each fill-up: date, odometer, fuel amount, price and cost. It's used to calculate real fuel economy and running costs.
Why should I keep a fuel log?
To know your real economy and costs, budget accurately, and spot mechanical problems early when economy drops.
Do I need to fill up completely every time?
For accurate economy, yes, at least on the fill-ups you use for the calculation. Record partial fills but mark them.
What's the best fuel log app?
It depends on your needs. CarO combines a fuel log with maintenance and expenses; see our fuel log apps comparison for others.
Can I track EV charging in a fuel log?
Yes, by logging kWh and cost per session in the same way.
Related guides
Track this in CarO
CarO is a free car maintenance tracker app for iPhone and Android that keeps a full service history, reminds you about oil changes and inspections by mileage or date, and logs fuel fill-ups with MPG, odometer readings and car expenses for every vehicle you own. Logs are stored in the cloud and can be exported as CSV.
