What this calculator does
Travelling time by car is rarely just distance divided by speed limit. This calculator starts from that basic driving-time figure, distance divided by the average speed the trip is likely to hold, and then adds a percentage allowance on top for traffic, fuel stops, meal breaks and the other slowdowns that a straight-line calculation ignores.
The average speed matters more than it looks. It is not the speed limit, but the realistic pace once intersections, roundabouts, overtaking and lower-speed sections are averaged out over the whole trip, which is usually well under the posted limit on anything other than an open motorway.
The formula
Driving time is distance divided by average speed. The allowance is then applied as a percentage on top of that driving time to account for traffic, stops and breaks that are not part of the raw distance-over-speed sum, giving a total travel time that is closer to what the trip actually takes door to door.
| Term | Meaning |
|---|---|
| Driving time | Distance divided by average speed, with no allowance added. |
| Allowance | A percentage added to driving time to cover traffic, fuel and rest stops. |
| Total travel time | Driving time plus the allowance, the more realistic door-to-door figure. |
The inputs explained
| Field | What to enter |
|---|---|
| Distance to travel (km) | The distance to be travelled, by road rather than a straight-line distance. |
| Average speed (km/h) | The average speed expected for the whole trip, not the speed limit. A mix of motorway and town driving will average well below the top speed limit on any single stretch. |
| Traffic and rest-stop allowance (%) | An allowance added on top of the raw driving time for traffic, fuel stops and rest breaks. Fifteen per cent is a reasonable starting point for an ordinary trip; a longer trip with several stops planned would need more. |
When to use it
Planning a road trip departure time
Working backwards from an arrival deadline, the total travel time including the allowance gives a more realistic departure time than the raw distance-over-speed figure alone.
Comparing routes
Two routes with the same distance can have different average speeds, one mostly motorway and one through several towns, and comparing the resulting travel times shows which is actually faster rather than just shorter.
Budgeting a delivery or commute schedule
Adding a consistent allowance for traffic across every trip in a schedule avoids the optimistic bias that comes from planning purely off distance and speed limit.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How total travel time changes with distance, at a fixed average speed and allowance
The same average speed and allowance, across a range of trip distances.
| Distance | Estimated total travel time | Driving time at this speed |
|---|---|---|
| 50 km | 0 h 38 min | 0 h 33 min |
| 100 km | 1 h 16 min | 1 h 6 min |
| 200 km | 2 h 33 min | 2 h 13 min |
| 300 km | 3 h 50 min | 3 h 20 min |
| 500 km | 6 h 23 min | 5 h 33 min |
| 800 km | 10 h 13 min | 8 h 53 min |
How the allowance changes total travel time on a 300 km trip
A fixed distance and speed, with the traffic and rest-stop allowance varied.
| Allowance | Estimated total travel time | Extra time from allowance |
|---|---|---|
| 0% | 3 h 20 min | 0 h 0 min |
| 10% | 3 h 40 min | 0 h 20 min |
| 15% | 3 h 50 min | 0 h 30 min |
| 20% | 4 h 0 min | 0 h 40 min |
| 30% | 4 h 20 min | 1 h 0 min |
| 50% | 5 h 0 min | 1 h 40 min |
Questions
What average speed should I use?
Use the realistic pace for the whole trip, not the highest speed limit along the route. A trip that mixes motorway and town driving typically averages well below the motorway limit once intersections, traffic and lower-speed sections are factored in.
How big should the traffic and rest allowance be?
It depends on the route and time of day. Fifteen per cent is a reasonable default for an ordinary trip with light traffic; peak-hour city driving or a long trip with several planned stops warrants a larger allowance.
Does this calculator use live traffic data?
No. It applies whatever allowance percentage is entered on top of the raw driving time, rather than pulling live conditions, so the allowance should be set to reflect the traffic expected for that specific trip and time.
Why is my actual trip always longer than the estimate?
The most common cause is an average speed that is set too high, closer to the speed limit than the realistic pace once stops, traffic and slower sections are included. Lowering the average speed input, or increasing the allowance, brings the estimate closer to what the trip actually takes.
To work out an average speed from a distance and time already travelled, see the average speed calculator. For converting the resulting travel time between minutes and hours, use the minutes to hours calculator.