You are driving a 20-mile commute. How much time do you actually save by speeding at 80mph instead of 65mph?

Why 15 mph faster saves only a few minutes

At a constant 65 mph, covering 20 miles takes about 18 minutes 28 seconds. At 80 mph, it takes exactly 15 minutes. The difference is about 3 minutes 28 seconds—assuming you can hold either speed for the entire trip.

The reason is that travel time depends on both speed and distance: time equals distance divided by speed. Raising speed by about 23 percent does not cut the trip time by 23 percent; over a fixed distance, it cuts it by about 19 percent.

The road rarely lets you hold a steady speed

Those figures are best-case arithmetic, not a promise about a commute. Traffic, signals, curves, merging, and slowdowns can prevent a driver from maintaining either speed. A brief burst at 80 mph saves less than the calculation suggests, and any delay elsewhere can erase a few minutes of potential gain.

So the practical payoff of going 15 mph faster on this stretch is modest: less than three and a half minutes, even with an uninterrupted run. That is the time budget before accounting for the need to slow down or stop.