Daylight Hours Calculator: Plan Your Hike Before Dark on iPhone
Last updated 2 June 2026
To work out how much daylight you have for a hike without a connection, use the offline Daylight Calculator in FOC. You pick a month and set your latitude on a slider, and it estimates the daylight duration in hours along with an approximate sunrise and sunset time. That gives you a rough window to plan your route and reach camp before dark, all on your iPhone with no signal and no GPS lookup needed.
The numbers are estimates, not a precise astronomical almanac. The app says as much: calculated times may differ from actual values. Treat them as a planning aid, then leave yourself a margin.
How the Daylight Calculator works
The calculator takes two inputs and returns a daylight window. There is no location lookup and no internet call, so it works the same in a valley with no bars as it does at home.
- Month. You choose the month from a picker. Each month carries a baseline daylight figure, short in midwinter and long around midsummer, reflecting how the day length swings through the year.
- Latitude. You set your latitude on a slider yourself. It does not read your position automatically. Moving further from the equator stretches summer days and shortens winter ones, and the estimate shifts to match.
From those two values the tool shows the daylight duration in hours, plus an approximate sunrise and sunset. It builds those times by centering the daylight around midday, so sunrise sits as far before noon as sunset sits after it. That keeps the model simple and offline, at the cost of the small real-world shifts that time zones, daylight saving, and your exact longitude introduce.
Using it to reach camp before dark
The point of the tool is a quick gut check before you commit to a route. A worked example:
- Set the month to when you are actually hiking, and set the latitude slider near where you are.
- Read the daylight duration and the estimated sunset.
- Count back from sunset by the time your route is likely to take, then add a buffer for breaks, navigation, and going slower than planned.
- If your start time plus the route falls after that buffer, shorten the day, start earlier, or plan to camp sooner.
Because it is an estimate, give yourself margin rather than treating the sunset time as exact. The app itself flags this: the calculated times are estimates and may differ from actual values. Pair it with your own headlamp and a sensible turnaround time. For the wider picture before you set out, see Before you go off-grid and the broader Hiking and backpacking skills guide. When the light does run out and you need to keep moving, Navigate without a compass covers reading direction without instruments.
How it compares
| Factor | FOC Daylight Calculator | Working it out by hand |
|---|---|---|
| Connection needed | None, fully offline | None, but you need a printed table or memory |
| Inputs | Month picker and a latitude slider | You look up the date and your latitude yourself |
| Output | Daylight hours plus approximate sunrise and sunset | Whatever you can read off a chart or recall |
| Precision | An estimate, flagged as such in the app | Depends entirely on your source |
| Speed in the field | A few taps on your iPhone | Slower, and easy to get wrong under pressure |
| Cost and tracking | Free, no ads, no in-app purchases, no tracking | Free if you carry the reference |
Frequently asked questions
Does the Daylight Calculator use my GPS or location?
No. You set the latitude yourself on a slider and choose the month from a picker. The tool never reads your position or goes online, which is why it works with no signal.
How accurate are the sunrise and sunset times?
They are estimates. The app states that calculated times may differ from actual values. It centers daylight around midday and adjusts by month and latitude, so use the result for planning and leave yourself a margin rather than treating it as exact.
Does it work without any internet connection?
Yes. The Daylight Calculator is part of FOC's offline reference and runs entirely on your iPhone. There is no network request, so it behaves the same deep in the backcountry as it does at home.
What do I need to enter to get a result?
Just two things: the month you are hiking and your latitude, which you set on a slider. From those the tool estimates the daylight duration in hours and an approximate sunrise and sunset.
Does FOC cost anything or show ads to use this?
No. FOC is free, with no ads, no in-app purchases, and no tracking. The Daylight Calculator and the rest of the reference are available without any account or payment.
Related
Sources
This is general reference, not medical, safety, or professional advice. Skills like first aid and foraging carry real risk. In a real emergency, call your local emergency number (112 in the EU, 911 in the US).