A walking-time estimate tells you how long a route should take. Turning that into a good day out means fitting it around three other things: the daylight you have, the pace of your slowest walker, and a point at which you'll turn back whatever happens. This guide covers each one.
Work back from sunset
In the British winter, daylight is short. In December much of Scotland gets around seven hours of usable light, and even southern England only about eight. A route that takes six hours on paper leaves very little margin. The safest approach is to plan backwards. Start from sunset, subtract an hour of safety margin, subtract your estimated walking time plus breaks, and that's your latest start time. If the start time comes out earlier than you can realistically leave, pick a shorter route.
Summer gives far more room, but long days bring their own risk: it's easy to keep going because it's still light, then run out of energy rather than daylight.
Plan for the slowest walker
Naismith's rule and its variations assume a fit adult on decent paths. Groups move at the speed of their slowest member, and children, new walkers and heavy packs all slow a group down. A useful habit is to calculate the time with a pace that suits the slowest person, then add more break time than you think you need: around ten minutes an hour for a mixed group is realistic, more with young children. The walking time calculator lets you set your own pace and break allowance.
Set a turnaround time
Before you start, agree a time at which you'll turn back, even if you haven't reached the summit or the halfway point. Mountain rescue teams in Britain are regularly called to people who pressed on past the point where they could get down in daylight or before the weather turned. A turnaround time takes the decision out of the moment, when tiredness and the wish to finish make it hard to judge.
A simple version works well: if you haven't reached the halfway point by the time you've used half your available daylight, turn around.
Check the forecast for where you're going
Valley forecasts can be very different from conditions on high ground. Wind speeds rise with height, and temperatures fall by around one degree for every 150 metres of climb, before wind chill. The Met Office publishes specialist mountain forecasts for the main upland areas, which are worth checking the evening before and the morning of your walk.
Tell someone your plan
Finally, leave your route and expected return time with someone who isn't walking with you, and tell them what to do if you're late. It costs nothing and gives rescuers a head start if anything goes wrong. With a sensible time estimate, a daylight plan and a turnaround time, almost every walk ends the way it should: tired, happy and back before dark.