- Compliance fuel economy uses the EPA's 2-cycle city and highway tests, weighted 55% city / 45% highway. Label values add high-speed, air-conditioning and cold-temperature tests, the 5-cycle method, to capture a wider range of driving conditions.
- The EPA has changed its label method three times: in 1985 (multipliers of 0.9 for city and 0.78 for highway on the 2-cycle results), in 2008 (the 5-cycle method) and in 2017 (updated 5-cycle equations). When it adopted the 5-cycle method the EPA projected label values about 11% lower for city and 8% lower for highway.
- The label's combined MPG is still weighted 55% city / 45% highway, but the EPA's real-world estimates in its Trends report use 43% city / 57% highway, which it says matches fleetwide driver activity data.
- For electric vehicles, MPGe converts energy use to a gasoline-equivalent basis; in FuelEconomy.gov data one gallon-equivalent works out to about 33.7 kWh.
01 Introduction
The number on a new vehicle's fuel economy label is not one measurement. It is built from laboratory tests, adjusted, and then combined with a fixed city / highway weighting. Understanding those steps explains why the fuel economy you see on the road can differ from the label.
EPA, Automotive Trends Report 2025, Section I.C (Fuel Economy Metrics in this Report) and Appendix C02 2-Cycle vs 5-Cycle Testing
The EPA and NHTSA measure fuel economy for CAFE compliance with the EPA's city and highway test procedures, called the 2-cycle tests, and weight the results 55% city and 45% highway. The EPA notes that these procedures are required by law for CAFE but no longer accurately reflect real-world driving.
EPA, Automotive Trends Report 2025, Section I.CThe 5-cycle method adds tests for high speeds (US06), air conditioning (SC03) and cold temperature to the two basic city and highway tests. Together they capture a wider range of operating conditions, including hot and cold weather, higher speeds and faster accelerations. The city and highway values on the label are 5-cycle values.
EPA, Automotive Trends Report 2025, Section I.C and Appendix DThe table below shows the same vehicle measured three ways, using the EPA's own example of the model year 2024 Toyota Prius:
| Metric | Purpose | City / Hwy Weighting | Combined MPG | City MPG | Highway MPG |
|---|---|---|---|---|---|
| 2-cycle (unadjusted) | Manufacturer compliance | 55% / 45% | 80 | 83 | 78 |
| Label | Consumer information | 55% / 45% | 57 | 57 | 56 |
| Estimated real-world | Best estimate of real-world performance | 43% / 57% | 56 | 57 | 56 |
The five test cycles differ in speed, acceleration, temperature and air-conditioner use:
| Attribute | City | Highway | High Speed | Air Conditioner | Cold Temp |
|---|---|---|---|---|---|
| Top speed | 56 mph | 60 mph | 80 mph | 54.8 mph | 56 mph |
| Average speed | 20 mph | 48 mph | 48 mph | 22 mph | 20 mph |
| Max. acceleration | 3.3 mph/s | 3.2 mph/s | 8.46 mph/s | 5.1 mph/s | 3.3 mph/s |
| Simulated distance | 11 mi | 10 mi | 8 mi | 3.6 mi | 11 mi |
| Time | 31 min | 12.5 min | 10 min | 9.9 min | 31 min |
| Stops | 23 | None | 4 | 5 | 23 |
| Idling time | 18% | None | 7% | 19% | 18% |
| Engine start | Cold | Warm | Warm | Warm | Cold |
| Lab temperature | 68–86°F | 68–86°F | 68–86°F | 95°F | 20°F |
| Air conditioning | Off | Off | Off | On | Off |
Estimate your vehicle's driving cost using official EPA fuel economy data.
Use the Calculator03 Three Label Changes
The EPA has updated its label methodology three times, for model years 1985, 2008 and 2017. In 1985 it began applying multipliers of 0.9 for city and 0.78 for highway to the 2-cycle results, because real-world fuel economy had been diverging from the laboratory numbers. In 2008 the 5-cycle method replaced those universal multipliers; in the 2006 rulemaking the EPA projected an average fleetwide adjustment of 11% lower for city and 8% lower for highway fuel economy. In 2017 the label equations were updated again using test data from model year 2011 to 2016 vehicles.
EPA, Automotive Trends Report 2025, Appendix D (Historical Changes in the Database and Methodology)04 City vs Highway Ratings
A new vehicle label shows city, highway and combined values. The label's combined rating is the harmonic average of the city and highway values with a 55% city / 45% highway weighting.
EPA, Automotive Trends Report 2025, Appendix CThe harmonic mean is used because MPG is a ratio: a vehicle that gets half the MPG uses twice the fuel. A vehicle rated 25 city / 35 highway does not get 30 combined:
The combined value (28.7 MPG) is lower than the simple average (30.0 MPG) because the less efficient city driving has a disproportionate effect on fuel used.
Arithmetic example using the EPA, Automotive Trends Report 2025 definition of the label combined value05 MPGe for Electric Vehicles
Electric vehicles do not burn fuel, so the EPA rates them in MPGe (miles per gallon equivalent) to allow energy efficiency comparisons with gasoline vehicles. The conversion is based on the energy content of a gallon of gasoline:
FuelEconomy.gov data (vehicles.csv, model years 1984 to 2026): for the 1,437 all-electric configurations, combined MPGe multiplied by kWh per 100 miles and divided by 100 has a median of 33.7 kWh per gallon-equivalent.For example, a vehicle that uses 25 kWh per 100 miles converts as 33.7 / 0.25 = 135 MPGe, the energy equivalent of about 0.74 gallons of gasoline per 100 miles.
Arithmetic example using the median conversion derived from FuelEconomy.gov dataHowever, MPGe does not directly translate to fuel cost. The cost to "fuel" an EV depends on local electricity rates, which vary from about 11.5 cents per kWh in the cheapest state to nearly 43 cents per kWh in Hawaii. A high MPGe vehicle is energy efficient, but whether it is cheaper to operate depends on the ratio of electricity prices to gasoline prices in your area.
EIA Form 861 Table 5A (2024): residential electricity prices range from 11.5¢/kWh (North Dakota) to 42.9¢/kWh (Hawaii); California is second-highest at 32.0¢/kWh06 Data Sources
- U.S. EPA. The 2025 EPA Automotive Trends Report (EPA-420-R-26-001): Section I.C, Appendices C and D. epa.gov
- ORNL/DOE. Transportation Energy Data Book, Edition 40, Table 4.35 (driving cycle attributes). tedb.ornl.gov
- EPA/DOE. Fuel Economy Guide vehicle data (vehicles.csv). fueleconomy.gov
- EIA. Form EIA-861, Table 5A (2024), average residential electricity price by state. eia.gov