How to Use the Highway vs City Fuel Economy Calculator
The same car can get very different real-world gas mileage depending on whether you mostly drive highway or city streets. This calculator takes your highway driving share along with separate highway and city MPG figures, combines them using a harmonic mean, and estimates your monthly fuel cost from your driving distance and local gas price.
Combined MPG isn't a simple average of the two numbers — it has to be weighted by how much fuel you actually burn in each condition, which is why the harmonic mean gives a more accurate result. Since steady highway speeds are usually more efficient than stop-and-go city traffic, a higher highway share typically pushes your combined MPG up and your fuel bill down.
Your EPA window sticker MPG is measured under standardized test conditions, so it often doesn't match what you see at the pump — AC or heater use, aggressive driving, and traffic all pull real mileage down. For the most accurate estimate, enter MPG figures you've calculated yourself from recent fill-ups rather than the sticker numbers.
Frequently Asked Questions
No, it's a weighted harmonic mean based on your actual driving mix, not a simple average. This method matches real fuel usage and mileage far more accurately than averaging the two numbers directly.
EPA ratings are measured under controlled test conditions, while real driving involves AC or heater use, hard acceleration and braking, and traffic — all of which lower fuel economy. Enter your own measured MPG here for a more accurate result.
Usually, yes. Steady-speed highway driving tends to get better mileage than stop-and-go city traffic, so a higher highway share generally improves your combined MPG and lowers your fuel spend.