⛰️ Turnaround Time Calculator
The latest moment you can still be going up. Enter where you are, when you set off and what the route costs, and get the time to turn back — against sunset on your clock, not the sundial's.
🧭 Where, when, and how far
The hour of daylight that isn't there
This site already has a daylight calculator and a hike time calculator. Between them they hold everything needed to answer the question that actually matters on a hill, and neither answers it, because the answer needs both halves and a correction that sits between them.
The daylight page reports solar time, and says so plainly in its own notes. Solar noon is the moment the sun is highest above your head; the clock on your wrist keeps mean time for a whole timezone. Two things separate them. The equation of time— the Earth's orbit is an ellipse and its axis is tilted, so the sun runs up to about sixteen minutes fast or slow depending on the date, and is exactly right only four days a year. And longitude— four minutes for every degree you sit away from your timezone's meridian.
Those two can add to more than an hour. A plan built on “sunset at six” when your watch will say five past five is not a cautious plan with a small error in it; it is a plan with its entire safety margin already spent. This page does that arithmetic so the turnaround time you write on the back of your hand is the one your watch will agree with.
❓ Frequently Asked Questions
What is a turnaround time?
The latest clock time at which you can still be going up and still get back down with daylight in hand. It is fixed before you leave, and it is honoured regardless of how close the summit looks — that is the entire point of setting one. Most benightments are not navigation failures; they are people who kept going for another twenty minutes, four times.
Why doesn't the daylight calculator already answer this?
It gives sunset in SOLAR time, and says so in its own notes. Solar noon is when the sun is highest where you are standing, which is not when your watch says twelve. Two corrections separate them: the equation of time, worth up to about sixteen minutes either way depending on the date, and your longitude within your timezone, worth four minutes for every degree. At the western edge of a wide timezone those combine to over an hour — an hour of daylight a plan can assume it has and simply does not.
How is the walking time worked out?
Naismith's rule, using the same figures as our hike time calculator, so the two pages agree: a fixed pace over the horizontal distance plus extra time for the climb. The descent leg keeps your walking pace but drops the climbing penalty, which is the standard Naismith return assumption. It is not a claim that descending is effortless — only that you do not pay for it at the ascent rate.
What margin should I leave?
The default is forty-five minutes of daylight still in hand when you reach the car. Increase it for unfamiliar ground, a party with mixed pace, loose descent, or any route where the last section is steep or requires care. The margin is what absorbs a twisted ankle, a wrong turn, or a slower companion — the things that actually make people late.
Does this account for twilight?
No, and deliberately. It works to sunset, not to the end of civil twilight, because useful light on a rough descent goes long before the last glow leaves the sky — and under cloud or in a forest it goes sooner still. Treating twilight as walking time is how a comfortable margin becomes no margin.