Drive Time Calculator

Distance divided by average speed

Drive time is distance divided by speed, and every other detail is an adjustment to those two numbers. Sixty miles at 60 mph is one hour. Ninety miles at 45 mph is two hours. The arithmetic is simple; the hard part is picking a speed that matches reality.

Most trips are not one speed. A 120 mile trip might be 90 miles of interstate at 65 and 30 miles of city streets at 25. Treating that as one average of 60 mph gives 2 hours, and the real answer is 2 hours 35 minutes. Splitting the trip into a highway leg and a city leg is the single change that makes an estimate usable.

The formula for each leg is minutes equals miles divided by miles per hour, times 60. For the highway leg, 90 divided by 65 is 1.385 hours, which is 83 minutes. For the city leg, 30 divided by 25 is 1.2 hours, or 72 minutes. Add them and you have 155 minutes of driving before a single stop.

Then add the stops, because they are time on the clock even though they are not time behind the wheel. A 15 minute fuel stop turns 155 minutes into 170, which is 2 hours 50 minutes. The gap between the two numbers is the part people forget when they plan a departure.

The speed limit is not your average speed

A 65 mph sign does not mean 65 miles every hour. It means 65 is the maximum when conditions allow, and the average over a real trip is always lower. Three things pull it down.

• City driving. Signals, stop signs, turns and parking lot exits cut the average hard. A 25 mph arterial with a light every quarter mile averages 15 to 20.
• Traffic. Congestion does not just slow you, it removes the recovery time. Ten minutes at 5 mph costs more than ten minutes of lost distance.
• Everything else. Construction zones, toll plazas, trucks passing, weather and the two minutes you lose at every fuel stop.

FHWA measures this with the travel time index, which compares a trip at peak hours to the same trip in free flow. In the 52 largest metro areas the interstate index averaged 1.34, according to the FHWA Conditions and Performance report, which means a 30 minute free flow trip takes about 40 minutes at peak.

That is the number to hold onto when a mapping app shows an arrival time an hour before yours. The app is using live data and you are using an assumption, and the assumption needs to be honest about the city miles.

Worked example: 120 miles with 30 in town

A trip with 90 highway miles at 65 mph and 30 city miles at 25 mph, one 15 minute stop, leaving at 8:00 AM.

• Highway: 90 / 65 x 60 = 83 minutes
• City: 30 / 25 x 60 = 72 minutes
• Driving time: 155 minutes, or 2 hours 35 minutes
• Stop: 15 minutes
• Total trip: 170 minutes, or 2 hours 50 minutes
• Effective average speed: 120 / 2.83 = 42.3 mph
• Arrival: 8:00 AM + 2 hours 50 = 10:50 AM

The effective average of 42.3 mph is the number worth noticing. The highway leg ran at 65 and the trip as a whole ran at 42, because a quarter of the miles were city miles at 25 and the stop took another 15 minutes. That gap between the sign and the average is where most bad arrival estimates come from.

Now imagine the same trip on a holiday weekend with a 20% slowdown. Highway speed drops to 52 and city to 20, so the legs become 104 and 90 minutes. Driving time is 194 minutes, the stop brings it to 209, and the arrival moves from 10:50 to 11:29. Thirty-nine minutes, from traffic alone.

Traffic: what a slowdown costs

A percentage slowdown is an easy way to model congestion without live data, and the result is not linear. A 20% cut in average speed adds 25% to the time, because time is inversely proportional to speed. That is why a modest-looking slowdown produces a large-looking delay.

The table holds the stop at zero so the slowdown is the only variable. The 46.4 mph baseline is the driving average without the stop; add the 15 minutes back and the effective average falls to 42.3.

Two practical uses. First, plan the departure around the congestion rather than through it: leaving at 6:00 AM instead of 8:00 can remove most of the city leg's penalty. Second, when a mapping app gives you a range instead of a single arrival time, the long end of the range is usually the 20% to 30% case, and that is the one to plan a connection or a dinner reservation around.

Stops, fuel and food

Stops are cheap individually and expensive in total. A 15 minute stop every two hours on a 10 hour drive adds 75 minutes, which is more than an hour of daylight lost.

The difference between a 10 minute stop and a 25 minute stop, four times over, is an hour. That is the same hour you would gain by driving 10 mph faster for the whole trip, and the stops are far safer.

Rest is not optional on a long drive. NHTSA's drowsy driving guidance reports 644 deaths from drowsy-driving crashes in 2024 and recommends a 20 minute nap at a rest area when you start to feel sleepy, which is longer than a fuel stop and worth planning for. The agency also notes that at 55 mph a four to five second micro sleep covers more than 100 yards. Build the breaks into the plan rather than discovering them.

Average speed by road type

Picking the speed is the part that decides whether the estimate is useful. The table below gives realistic averages, not limits, for the kinds of road a US trip uses.

The last two rows explain most of the surprises. Ten miles of rush hour city street takes 50 minutes, which is more than 50 miles of rural interstate. If a trip starts or ends inside a city, that leg deserves its own line in the calculation rather than being folded into an overall average.

For a long interstate run, 65 is a fair planning number in the West and 60 is fairer in the Northeast, where traffic and tolls take a bigger bite. Two lane highways with towns every few miles average 50 to 55. Mountain roads with switchbacks average 35 to 45, and weather can halve that.

Leaving time and arrival

An arrival time is a departure time plus a total trip time, and the arithmetic is the easy part. The judgment is in the buffer.

For a drive where you need to be somewhere at a fixed time, add 15% to the estimate or 20 minutes, whichever is larger. That covers a fuel stop that runs long, a construction backup and a wrong turn. For a 2 hour 50 minute trip, the buffer is 25 minutes, which puts the departure at 7:35 for a 10:50 arrival.

Time zones are the other trap. Crossing into a zone an hour ahead moves your arrival clock forward by an hour, so a 2 hour 50 minute drive that leaves at 8:00 AM arrives at 11:50 local, not 10:50. Arizona is the exception that catches people, since it does not observe daylight saving time and sits an hour off its neighbors for half the year.

Departure time also changes the traffic you meet. Leaving at 5:30 AM puts the city leg before the morning peak, and leaving at 10:00 AM puts it after. On a 120 mile trip with 30 city miles, that choice is worth 30 to 40 minutes, which is more than any reasonable change in highway speed.

When to split the drive in two

There is a distance past which the arithmetic stops being the point. For a single driver, that is around 8 hours or 500 miles in a day, and the second day of a two day trip is always easier than the last two hours of a one day trip.

The numbers behind the rule are about attention rather than stamina. Reaction time, lane keeping and hazard detection all degrade with hours behind the wheel, and the degradation is worse in the afternoon and after dark. A 12 hour day driven by one person ends with the driver least capable at the point of highest fatigue.

Two 6 hour days also cost less than they look. A hotel night is $100 to $150, against the fuel and food of pushing through, and the arrival is earlier on day two than it would be at the end of a marathon day. If the trip is 900 miles, two 450 mile days at 7.5 hours each is the sane plan, and three 300 mile days is better still if the schedule allows.

For a two driver household the limit roughly doubles, but the stops do not. Rotate every 2 hours so the passenger can rest properly, and treat the swap as a stop that counts toward the break schedule rather than instead of it.