Tracking Online or On Paper Shows True Fuel-Economy NumbersDo you know what kind of fuel economy your car gets? You might have a rough idea based on the Environmental Protection Agency (EPA) estimates listed on the car's window sticker. Or maybe you have a sense of the gas mileage from how often you fill up and how much gas the tank holds. But to really know where you stand, you have to keep accurate records. The results might surprise you.

If you regularly start computing your fuel efficiency, you can find ways to save money on gas and know how to budget for the future. You can modify your driving habits and see what kind of improvements that makes in gas mileage. And maybe you'll find this recordkeeping fun.

There are two ways to approach fuel-economy tracking: online and old school.

The online approach is simple. Sign up with a Web site dedicated to mileage tracking. There are several out there including MPGTune.com and Fuelly.com. You enter via your computer or smartphone and all the sites do all the computational work for you. Some sites let you compare your car's performance with other users who drive cars of the same make, year and model as yours.

If you decide to use the paper-and-pen route (which is what we do here at Edmunds with our long-term test cars), there are a few things you'll need to do to get started. The first step is to buy a small notebook and keep it, along with a pen, in the door panel of your car. Create six columns in the notebook and label them in this order: date, odometer, trip, gallons, MPG, notes.

Date: This is the date you buy gas. This will help you budget for gas by showing you how often you fill up the tank.