Outdoor Calculators
Back before dark.
Enter where and when you are hiking, when you set off, and how long the hike takes each way. Get sunrise, sunset, the end of civil twilight, whether you finish in daylight, and the latest start and turnaround time. Computed in your browser with NOAA solar equations; nothing is sent.
Worked example
Toronto (43.65 N, 79.38 W) on June 21, UTC-4. Sunrise 05:36, sunset 21:03, end of civil twilight 21:39. A hike that starts at 15:00 with 2 h out and 2 h back finishes at 19:00, 2 h 03 min before sunset. With a 30 minute buffer, the latest start is 16:33 and the latest turnaround is 18:33. On December 21 the same hike has only 9 hours of daylight: sunset is 16:44.
How it works
Sunrise, sunset and civil twilight come from the NOAA solar position equations (after Jean Meeus, Astronomical Algorithms): the equation of time and solar declination from the date give the hour angle H where cos H = (cos Z - sin lat x sin dec) / (cos lat x cos dec). The zenith Z is 90.833 degrees for sunrise and sunset (atmospheric refraction plus the sun's radius) and 96 degrees for the end of civil twilight. Accuracy is about 1 to 2 minutes at mid-latitudes, and it ignores terrain and elevation.
Latest start = sunset - buffer - (hours out + hours back). Latest turnaround = sunset - buffer - hours back. Hours out and back are your own estimates; use the Tobler or Naismith calculators to get them. Polar latitudes are not supported.
Sources and basis: NOAA Global Monitoring Laboratory solar calculation equations (Jean Meeus, Astronomical Algorithms); verified against published sunrise and sunset tables for Toronto. Checked 2026-10-05. Planning guide only, not medical or safety advice. Conditions, health and equipment change real needs; use your own judgment and local guidance.
FAQ
What time should I start a hike to finish before sunset?
Subtract your hiking time out and back, and a buffer of at least 30 minutes, from sunset. The calculator shows that as the latest start.
What is a turnaround time?
A fixed clock time at which you turn back whether or not you reached the goal. Setting it from sunset and your return time keeps you from finishing in the dark.
What is civil twilight?
The period after sunset until the sun is 6 degrees below the horizon. In clear weather there is enough light to see outdoors without a lamp at the start of it, and it is nearly dark by the end.
Does this work offline?
Yes. The calculation runs in your browser. You type your coordinates yourself and they are never sent anywhere. The tool does not ask your device for its location.
How accurate is it?
Within about 1 to 2 minutes of published tables at mid-latitudes on level ground. Hills, valleys and tree cover make local dark come earlier.