Why EPA Ratings Change by Model Year (2008 Re-Rating, Carryover)

A model’s EPA rating can differ from one model year to the next for three reasons: the vehicle itself changed, the EPA changed how ratings are calculated, or a rating was revised after the fact. The reverse also happens: many models have identical ratings in consecutive years because the test data was carried over. When you compare years, the safest comparison is within a single model year, or across years that were calculated with the same method.

Key takeaways

• Ratings belong to a model year. Compare 2007 models to 2007 models, as the EPA advised when it introduced the 2008 label.
• The EPA changed its method in 2008, and again updated its calculations for model year 2017.
• Manufacturers may carry over certification data from one model year to the next, so unchanged vehicles can show unchanged ratings.
• Labels can be corrected when information shows the values are too high.

The vehicle changed

A new engine, transmission, weight, tire or body shape changes the test result, and so the rating. The EPA also tests representative vehicles: manufacturers test one vehicle for each combination of loaded vehicle weight class, transmission class and basic engine, as fueleconomy.gov describes. A change in any of those creates a different test group. Size classes can shift as well, because class definitions use interior volume and weight ratings; see EPA vehicle size classes.

The method changed in 2008

The EPA updated its approach for model year 2008 to account for faster speeds and acceleration, air conditioner use and colder outside temperatures. fueleconomy.gov states that all of these factors lower fuel economy, and that the 2008 changes lowered fuel economy estimates for all vehicles. The EPA’s 2008 to 2012 label page says the revised label used new, more realistic methods and advised shoppers to compare models built in the same model year.

To keep older cars comparable, fueleconomy.gov adjusted estimates for model years 1984 to 2007 to be consistent with the 2008 method. That is why a 2005 vehicle’s MPG shown on fueleconomy.gov can differ from the number printed on its original window sticker. The EPA created a tool for converting older label values to the 2008 label format. The five test cycles that came out of this change are described in how the EPA tests fuel economy.

The calculation was updated in 2017

For model year 2017, the EPA updated some of the calculations used to estimate fuel economy rather than revising the test procedures again. The update used actual vehicle data from the 2011 to 2016 model years to better reflect today’s fleet, including technologies such as hybrids and turbocharged engines. fueleconomy.gov reports that most vehicles were not affected, that some estimates decreased by 1 mpg and a small number by 2 mpg. Estimates for some 2011 to 2016 vehicles were revised to match the new calculation, so those years can be compared with later ones. Ratings for model years 2008 to 2010 kept the earlier methodology.

Carryover: same vehicle, same rating

When a vehicle’s engine, transmission and weight class are unchanged, a manufacturer does not necessarily need to re-test it. EPA guidance letters state that manufacturers may carry over certification data from one year to the next, with applicable running-change data from the previous model year taken into account. The result is that a model can show an identical rating in consecutive model years. That is not an error or a copy-paste, but a consequence of how the data is produced.

On this site, that means a year-over-year table with identical rows is expected for some models, and a change between two years usually points to a real difference in the test group, or to a method change like the ones above.

Labels can be corrected

The EPA requires manufacturers to revise label values if relevant information shows that they are too high. The EPA monitors labels through independent testing of approximately 15% of vehicle models annually, in-use testing and information from consumer groups and industry. Reasons for past corrections include transmission software that optimizes performance during EPA tests but not in real-world driving, and underestimated aerodynamic drag and tire friction. A corrected rating applies going forward from the revised label.

Rules for who is rated change too

Which vehicles are rated at all changed in 2011. fueleconomy.gov states that, before 2011, vehicles with a GVWR over 8,500 pounds were exempt from testing; from 2011, passenger vehicles such as SUVs and passenger vans are exempt only at 10,000 pounds or more, while pickup trucks and cargo vans over 8,500 pounds remain exempt. A model that moved in or out of the rated group can therefore appear or disappear. See why heavy-duty pickups are not EPA-rated.

How to compare across years

• Prefer the same model year when comparing two vehicles.
• When comparing different years of the same model, check whether the vehicle changed (engine, transmission) and whether the years straddle a method change (2008 and 2017 are the two in this guide).
• Treat a 1 MPG difference between years as small, since labels are whole numbers and the underlying results can differ by less.
• Use Gallonly’s year-by-year tables on each model page, which show the EPA values for each model year; the methodology page says which data file we use and when it was published.
• For cost, remember prices change independently of ratings; see how annual fuel cost is calculated.

Real-world mileage will vary regardless of the rating; see real-world MPG vs the EPA label. Browse model years in the car database.