EPA is responsible for providing the fuel economy data that is used on the fuel economy label (or window sticker) on all new cars and light trucks. The data is also used by:

• The U.S. Department of Energy (DOE) to publish the annual Fuel Economy Guide;
• The U.S. Department of Transportation (DOT) to administer the Corporate Average Fuel Economy (CAFE) program; and
• The Internal Revenue Service (IRS) to collect Gas Guzzler taxes.

Updates to Fuel Economy Test Methods and Calculations

EPA periodically updates its methodology to account for changes in vehicle technologies, driver behavior, and/or driving conditions. The 2008 changes were broad revisions to the entire methodology that lowered the fuel economy estimates for all vehicles. The updates for 2017 will reduce some fuel economy estimates by 1 mpg and a small number by 2 mpg.

Model Year 2017 

EPA updated some of the calculations that manufacturers use to determine the EPA fuel economy label values. The update ensures that the label values are based on the newest and best data and science available. It also improves the accuracy of EPA’s label estimates by using data that better reflects the technologies available in today’s vehicle fleet. The updated calculations only reflect the evolving composition of the fleet and how new technologies respond to fuel economy testing. This update does not make changes based on driving behavior, ambient climate conditions, or other factors that are accounted for in the EPA methodology.

• The updated calculations use test data from 2011-2016 model year vehicles to inform the calculation of fuel economy estimates. The previous calculations were based on data from 2004-2006 model year vehicles. 
• To allow for proper comparison across all model years, MPG estimates on fueleconomy.gov have been revised for 2011-2016 model year vehicles to reflect the updated calculations.

All things being equal, this update will cause some MPG values to go down by 1-2 MPG relative to the previous calculations. However, auto manufacturers may make other changes from one model year to the next that also affect fuel economy values, such as using different tires or changing transmission shift logic. Not all changes to MPG values in 2017 models can be attributed to the updated calculations.

• EPA guidance letter #CD-15-15 (PDF) (8 pp, 520 K, June 22, 2015, About PDF)

Model Year 2008 

In 2006, EPA revised the test methods used to determine fuel economy estimates (city and highway) appearing on window stickers of all new cars and light trucks sold in the U.S. effective with 2008 model year vehicles. 

The test data is derived from vehicle testing done at EPA’s National Vehicle and Fuel Emissions Laboratory in Ann Arbor, Michigan, and by vehicle manufacturers who submit their own test data to EPA. 

Frequent Questions on Fuel Economy Testing and Labeling (PDF)(6 pp, 196 K, EPA-420-F-14-015, April 2014, About PDF)