How to use the latest trailhead start time calculator
- Enter the date of the hike, your latitude and longitude, and the UTC offset in effect that day.
- Enter your hiking time in hours and minutes, including breaks, and a safety buffer in minutes.
- Choose to finish before sunset or before last light, when the sun is 6 degrees below the horizon.
- Read the latest start time, and the sunrise, sunset and last light times it is based on.
Formula
Latest start = sunset (or last light) - hiking time - safety buffer
Sunset and last light come from the NOAA solar position formulas for the date, place and UTC offset
Sunset uses a solar zenith of 90.833 degrees and last light uses 96 degrees
Daylight available = sunset - sunrise
The NOAA formulas are described as accurate to within a minute for latitudes between 72 degrees north and south. Terrain and weather change the light you actually see.
Midsummer and midwinter near New York
In the New York area on 21 June 2026 (UTC-4) sunrise is 5:25 AM and sunset is 8:31 PM. A 4 hour 30 minute hike with a 30 minute buffer must start by 3:31 PM. On 21 December 2026 (UTC-5) sunset is 4:32 PM and last light is 5:03 PM, so a 3 hour hike with a 30 minute buffer that must end by last light must start by 1:33 PM.
Near Denver on 17 October 2026 (UTC-6) sunset is 6:17 PM, so a 6 hour 15 minute hike with a 45 minute buffer must start by 11:17 AM. A 20 hour route on the June day would need a start at 12:01 AM, before sunrise, and the page warns you.
Choosing the buffer
The buffer is the time you want to have left when you finish. A buffer makes up for slower pace, a wrong turn and stops. The right size depends on the trail, the group and the weather, so the page starts with 30 minutes as an example and lets you change it. If you carry a headlamp and are comfortable in the dark, finishing before last light instead of sunset gives more time.
To estimate how long a route takes, use the hiking time calculator. For sunrise, sunset and day length by date see the sunrise and sunset calculator, and the road trip time calculator helps with the drive to the trailhead.
What affects the real light
In a deep valley or on the east side of a ridge, the sun sets behind the terrain well before the time on the table. Dense forest and clouds darken the trail earlier. Enter the UTC offset that applies on that date, because the page does not know about daylight saving rules. Always tell someone your plan and carry the gear for the conditions.
Assumptions and limits
- The hike time is your own estimate for the whole route, including breaks.
- Sunset is the moment the top of the sun meets a flat horizon, with standard refraction.
- Last light is civil dusk, when the sun is 6 degrees below the horizon.
- Mountains, trees and weather are not modeled. At high latitudes the sun may not rise or set, and the page says so.
Frequently asked questions
How do I find the latest time to start a hike?
Take the time of sunset, subtract the hiking time and then a safety buffer. If sunset is 8:31 PM and the hike takes 4.5 hours with a 30 minute buffer, start by 3:31 PM.
Should I plan for sunset or last light?
Sunset is the safer choice without a light. Last light is about half an hour later at mid latitudes, and it assumes you have a headlamp and are comfortable using it.
What UTC offset do I enter?
The offset in effect on the date of the hike, including daylight saving time. New York is -4 in summer and -5 in winter.
Why does the page warn about a start before sunrise?
It means the hike plus the buffer is longer than the daylight, so you would begin in the dark. Pick a shorter route or plan for night travel.