What this planner works out
This planner divides distance by average speed to give driving time, then adds breaks at the interval and length you choose.
Average speed is the input that decides everything, and it is consistently overestimated. A journey at a 70 mph limit rarely averages anything close to it.
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Before you plan a departure time
- Average speed on a motorway journey including junctions and traffic is typically 50 to 60 mph, not 70. Mixed routes are considerably lower.
- Breaks are not optional on a long drive. Guidance recommends at least 15 minutes every two hours.
- The calculation does not know about traffic, roadworks or weather. Add a margin for all three.
- Departure time matters as much as distance. The same route at 8am and 11am can differ by an hour.
Driver fatigue is a factor in a substantial share of serious road collisions, and the highest-risk periods are the early hours and mid-afternoon. Sleepiness impairs reaction and judgement in ways that feel manageable and are not. The only genuine remedy is sleep — coffee and fresh air postpone the problem rather than solving it.
How this calculator works
Driving time plus scheduled breaks:
Driving time = distance ÷ average speed
Breaks taken = driving time ÷ break interval, rounded down
Total = driving time + (breaks × break length ÷ 60)Rounding the break count down means a journey just short of the interval takes no break, which matches how people actually drive rather than what would be ideal.
Worked example: 180 miles
Using the default figures — 180 miles at an average 55 mph, breaking 20 minutes every 2 hours:
- Driving time: 3.27 hours
- One break of 20 minutes
- Total: 3.6 hours
Three and a half hours for 180 miles, which is an average of 50 mph door to door. Planning the same journey at 70 mph gives 2.6 hours — an hour's difference, and the sort of optimism that turns an arrival time into a rushed drive. Adding a margin for traffic on top is the difference between a plan and a hope.
Common mistakes
- Using the speed limit as the average speed. Real averages are well below it.
- Skipping breaks to save time. Fatigue is a serious and underestimated risk.
- Ignoring the departure time. Traffic varies enormously through the day.
- Not allowing for the last mile. Urban approaches and parking take longer than expected.
- Planning to arrive exactly on time. Build in a margin.
Frequently asked questions
How often should I take a break?
Guidance recommends at least a 15 minute break every two hours on a long journey. Professional drivers are subject to legally enforced limits, and while private drivers are not, the physiology is identical. Sharing the driving where possible, and stopping when tiredness is first noticed rather than pushing on, are both more effective than any schedule.
What average speed should I assume?
For a motorway journey, 55 to 60 mph is realistic once junctions, services and traffic are included. For mixed A-roads, 40 to 45. For urban driving, 20 or less. Satnav estimates account for typical traffic and are usually better than a hand calculation for a specific route at a specific time.
Is it better to drive at night?
Roads are quieter, but the risk is higher. The body clock produces a strong dip in alertness in the early hours, and fatigue-related collisions cluster between about 2am and 6am. If a night drive is unavoidable, sleep properly beforehand and plan more frequent stops than you would by day.
What should I do if I feel sleepy?
Stop somewhere safe — never the hard shoulder except in an emergency. The recommended approach is a caffeinated drink followed by a short nap of 15 to 20 minutes, which allows the caffeine to take effect while you rest. Opening a window or turning up the radio does not work and should not be relied on.
Is what I enter stored?
No. Figures are processed in your browser and never transmitted or retained.
Related tools
References
- GOV.UK — Highway Code guidance on driver fatigue, breaks and road safety
- Health and Safety Executive — managing fatigue and driving for work
Sources are checked at publication and can change — how I choose and check references.