What Is a Turnaround Time and How Do You Set One?
A turnaround time is a clock time, decided before you leave, at which you stop going forward and head back, whether or not you have reached the summit, the lake or the viewpoint. Mountaineers use it on big peaks; it is just as useful on an ordinary day hike, because the most common way a good day goes wrong is simple: people keep going "just a bit further" and run out of daylight on the way down.
The Daylight Turnaround Calculator works one out from four things you already know: when you start, when the sun sets, how long the whole hike should take, and how much margin you want before sunset. This guide explains each step and works four days through it. All the times are hypothetical; use your own start time and the published sunset time for your date and place.
The four inputs
- Start time. When you actually leave the trailhead, not when you leave home.
- Sunset time. From a weather service or almanac for the date and location. In valleys and on east-facing slopes the sun drops behind ridges well before the official sunset, so treat this as the latest possible light, not a guarantee.
- Estimated round-trip hike time. From the Hiking Time Calculator plus your breaks. See Naismith's rule worked through for how to get a realistic figure.
- Safety buffer. How many minutes before sunset you want to be back at the car. The default is 60 minutes. The calculator puts the buffer before sunset because the dusk after sunset is not reliable walking light on rough ground.
There is a fifth setting, how much slower the way back is than the way out, which defaults to 25%. That one is the reason the turnaround is not at the halfway point, and it is worth understanding.
Why the turnaround is earlier than halfway
The obvious approach is to take the time between your start and your latest safe finish and turn around at the middle of it. That assumes the way back takes exactly as long as the way out. Usually it does not. By the afternoon you are tired, a careful descent on steep or loose ground is slow, the light is going, and you stop less willingly but more often.
The calculator therefore gives the return leg 25% more time than the outward leg by default. With the outward leg as 1 part and the return as 1.25 parts, the whole window is 2.25 parts, and the turnaround falls at 1 / 2.25 of the window, about 44% of the way through it rather than 50%. You can change the slowdown if your own logged hikes show something different, but it never goes below zero: the calculator will not assume you come back faster.
Every rounding goes the safe way. The latest safe finish and the turnaround round to the earlier minute; the projected finish rounds to the later minute.
Worked example: a standard day
Start 08:00, sunset 18:30, a six-hour hike including breaks, a 60-minute buffer and the default 25% slowdown. These are the calculator's default inputs.
- Latest safe finish: 18:30 minus 60 minutes = 17:30.
- Usable window: 08:00 to 17:30 = 570 minutes.
- Turnaround: 570 / 2.25 = 253 minutes after the start, so 12:13. That leaves 317 minutes for the way back.
- Projected finish: three hours out, then three hours times 1.25 back, so 14:45.
- Daylight margin: 17:30 minus 14:45 = 165 minutes.
On paper this is a comfortable day. If the hike goes to plan you reach your goal around 11:00, well before the 12:13 turnaround, and finish with nearly three hours in hand. The turnaround only matters if something slows you down, which is exactly when you need it decided in advance.
The same day with different assumptions
| Scenario | Turn back by | Projected finish | Margin |
|---|---|---|---|
| Standard: way back 25% slower | 12:13 | 14:45 | 165 min |
| Way back assumed as quick as way out (0%) | 12:45 | 14:00 | 210 min |
| Way back 40% slower | 11:57 | 15:12 | 138 min |
| Standard, but starting at 10:30 | 13:36 | 17:15 | 15 min |
Two lessons stand out. First, assuming an equal-speed return moves the turnaround half an hour later. That half hour is the difference between finishing in the light and finishing by headlamp if the day goes badly. Second, the late start barely moves the turnaround, from 12:13 to 13:36, but it destroys the margin. A six-hour hike started at 10:30 projects to finish at 17:15, a quarter of an hour before the latest safe finish. Any delay at all, a wrong turn, a twisted ankle, a long lunch, uses that up. The calculator still calls this plan safe because the margin is not negative, but a 15-minute margin is a plan with no slack, and a sensible response is to start earlier or choose a shorter route.
How to use it on the trail
- Decide it at home. Work out the turnaround the night before and write it down. Decisions made at the trailhead are made with excitement; decisions made at the turnaround point are made with summit fever.
- Tell the group. Everyone should know the time, and agree in advance that the clock decides, not the strongest walker.
- Set an alarm. A phone or watch alarm at the turnaround time removes the temptation to not look.
- Check progress against the plan. If you are well behind the estimate at the halfway point of the outward leg, the turnaround is likely to arrive before the goal does. Deciding to turn back early is a good decision, not a failure.
- Turn around when the time comes. Even if the top is ten minutes away. The mountain will be there another day.
What the turnaround does not cover
The calculator only knows about daylight. It does not know about:
- Weather. If thunderstorms are forecast, you need an earlier, weather-based cut-off; see planning to be down before afternoon storms. Turn back for weather whatever the clock says.
- How you feel. Exhaustion, cold, signs of heat illness, an injury or someone in the group struggling are all reasons to turn back before the turnaround time.
- Terrain hazards. A river that has risen, snow that has softened in the afternoon sun, or a section you would not want to descend in poor light.
- Getting lost. The plan assumes you stay on route.
Carry a headlamp with fresh or charged batteries on every hike, even one you expect to finish by lunchtime. Carry a map and a way to navigate, extra layers, food and water, and a first-aid kit. Tell someone your route and the time you expect to be back, so that someone will raise the alarm if you are not, and know the local emergency number. If you do end up behind schedule late in the day, our guide to what to do after your turnaround time has passed covers the options.