Whether you are planning a landscape shoot at golden hour, scheduling outdoor work around usable daylight, or simply curious why winter days feel so short, this day length calculator gives you precise, locally-timed sunrise and sunset data for any date and location — entirely offline in your browser.
What the calculator shows
For any combination of location and date the tool outputs:
- Sunrise and sunset in local clock time (applying the UTC offset you supply)
- Solar noon — the moment the sun reaches its highest point, when shadows are shortest
- Day length — total hours, minutes and seconds of daylight — plus the complementary night length displayed as a proportional bar
- Maximum solar elevation at noon, in degrees above the horizon
- Golden hour brackets — morning and evening — when the sun is within 6° of the horizon and light is warm and directional
- Civil twilight start (morning) and end (evening) — when useful outdoor light begins and ends beyond the official sunrise/sunset
For polar latitudes the tool correctly identifies midnight sun (sun never sets) and polar night (sun never rises) rather than producing nonsensical times.
The formula in plain terms
Day length depends on two quantities: the sun’s declination (how far north or south it is, which changes through the year) and your latitude. At the equinoxes the declination is 0° and every place on Earth gets almost exactly 12 hours. As the sun’s declination increases toward the summer solstice (23.5° N in June) northern latitudes gain extra daylight while southern ones lose it, and vice versa in December.
The key equation is the hour-angle formula:
cos H = (cos Z - sin φ · sin δ) / (cos φ · cos δ)
where H is the hour angle at sunrise (sunset is -H), Z is the solar zenith at the horizon (90.833°, accounting for refraction and the sun’s disc), φ is latitude and δ is the sun’s declination for that day. The day length in hours is simply 2H / 15 (since the sky rotates at 15° per hour). The Julian Day → Julian Century → mean longitude → mean anomaly → declination chain follows Jean Meeus, “Astronomical Algorithms”, 2nd edition.
Worked example
London (51.5° N), summer solstice (21 June):
- Julian Century for 21 Jun 2026 ≈ 0.2646
- Sun’s declination ≈ +23.4°
- cos H = (cos 90.833° - sin 51.5° · sin 23.4°) / (cos 51.5° · cos 23.4°) = (-0.01454 - 0.782 × 0.397) / (0.623 × 0.918) = (-0.01454 - 0.310) / 0.572 ≈ -0.571
- H = arccos(-0.571) ≈ 124.8°, day length = 2 × 124.8 / 15 ≈ 16.6 hours
The calculator gives sunrise at roughly 04:43 and sunset around 21:21 local BST — consistent with official UKHO tables.
Near the winter solstice the same formula gives roughly 7 h 50 min of daylight for London — under half the summer figure. The year-long chart makes this dramatic swing visible at a glance.
Tips for photographers
Golden hour is the window between civil twilight and 6° elevation — often only 20–40 minutes at mid-latitudes in summer, but stretching to well over an hour in winter when the sun climbs slowly. At high latitudes in summer the sun may stay within 6° of the horizon for hours, giving an extended golden glow. Toggle the year chart to find months where golden hour is longest at your location.