Most drivers know speeding can lead to tickets—but not everyone realizes it can drain your gas tank too. Driving faster than necessary is one of the easiest ways to reduce your fuel efficiency without even noticing. Whether you’re on a long highway stretch or zipping through city traffic, your speed plays a major role in how much fuel your engine burns.

So does speed really kill your MPG? In short—yes. Here’s why it matters, how much it impacts your mileage, and how to find the balance between getting there fast and saving money.

Speed vs. Efficiency: What the Data Says

Fuel economy isn’t a straight line. As your speed increases, your miles per gallon (MPG) decreases—especially once you pass a certain threshold. Most vehicles are designed to perform most efficiently at moderate speeds, where wind resistance and engine strain are minimized.

According to the U.S. Department of Energy, every 5 mph over 50 mph is like paying an extra $0.20 per gallon. That’s because aerodynamic drag increases exponentially with speed, meaning your engine has to work harder the faster you go.

The MPG Sweet Spot: 50–65 MPH

For most cars, the optimal cruising speed for fuel efficiency falls between 50 and 65 miles per hour. In this range, your engine runs in a balanced, low-strain zone and wind resistance stays manageable.

Driving at 70–80 mph? You could be losing 10–25% of your fuel efficiency compared to cruising at 60. The exact number varies by vehicle type and road conditions, but the pattern is clear: the faster you go, the more fuel you burn—and not in a linear way.

Real-World Comparison

Let’s say your car averages 32 MPG at 60 mph on the highway. At 75 mph, that might drop to 26 MPG. Over a 300-mile trip:

• At 60 mph: You’d use about 9.4 gallons
• At 75 mph: You’d use about 11.5 gallons

That’s a difference of over 2 gallons of fuel, or roughly $7–$10 depending on prices—just for arriving 45 minutes earlier.

For daily commuters, this adds up quickly. Even driving 5–10 mph slower during your regular highway stretch could lead to substantial monthly savings.

When It’s Worth Slowing Down

While it might not make sense to drive 50 mph on a 70 mph highway, here’s when reducing speed pays off most:

• Long highway trips where fuel efficiency compounds over time
• Driving in light traffic, where you can control your speed more consistently
• Hilly or windy terrain, where high speeds amplify resistance and strain

Pair that with steady driving habits like smooth acceleration and limited braking, and you’ll maximize your tank without significantly changing your routine.

Final Thoughts

Yes, speed really does kill your MPG—but that doesn’t mean you have to crawl in the right lane to save money. Simply knowing your car’s fuel efficiency sweet spot and dialing things back a few MPH on long drives can lead to measurable savings over time. Driving smarter, not slower, is the key to better mileage and fewer fill-ups.