Length of daylight calculator by date and latitude

It uses only the supplied values, performs the calculation with a standard solar declination and hour-angle formula, and never reads a clock or calls an outside service. The result is useful for planning, comparison, education, and data processing when a consistent approximation matters more than a location-specific astronomical almanac.

Enter an exact date and geographic latitude

Provide the date in strict ISO form, using four digits for the year followed by a two-digit month and day, such as 2026-06-21. Then provide latitude in decimal degrees from -90 to 90. Positive values describe places north of the equator, while negative values describe places south of it. Longitude and time zone are intentionally unnecessary because the requested quantity is the duration between the theoretical sunrise and sunset events, not their local clock times. The calculator validates the real Gregorian calendar, including the century rules for leap years, so impossible entries such as February 30 are rejected instead of silently adjusted. It also derives the ordinal day entirely through arithmetic. That makes an identical input produce an identical answer regardless of the computer, locale, current date, or UTC offset where it runs. Use a representative latitude for a city or site; moving farther north or south can materially change the estimate, especially near a solstice or inside a polar region. Decimal precision is accepted, but excessive coordinate precision does not make this approximate model an observatory-grade prediction.

Understand the solar approximation

The calculation first maps the calendar date to its day of year and estimates solar declination, the seasonal angle of the Sun north or south of Earth’s equator. It then applies the standard sunrise hour-angle relationship for the supplied latitude. Sunrise and sunset use a solar altitude of minus 0.833 degrees, a conventional correction that approximately accounts for atmospheric refraction and the visible radius of the Sun near the horizon. The resulting hour angle is converted into a duration over a 24-hour rotation and rounded to four decimal places for stable output. When the geometry says the Sun never drops below that conventional horizon, the response reports 24 hours and marks the condition as polar day. When it never rises above it, the response reports zero hours and marks polar night. All other cases are marked normal. This is a mathematical estimate: it does not model elevation, mountains, buildings, unusual atmospheric pressure, temperature, local terrain, or the small year-to-year changes represented by a full astronomical ephemeris.

Use the result with the right expectations

Treat daylight_hours as a consistent planning value rather than a promise of visible sunshine. Cloud cover does not alter astronomical day length, but terrain can hide the Sun after the formula’s idealized sunset or delay its appearance after idealized sunrise. At high latitudes, a small change in date or position may create a large change in duration, so calculate every date needed instead of extrapolating a whole season from one sample. The day_of_year field makes the calendar position explicit, and condition distinguishes ordinary sunrise-and-sunset geometry from polar edge cases. Because no longitude is requested, the capability does not return sunrise or sunset clock times; those depend on longitude, time zone, and civil-time rules. The deterministic approach is especially helpful in automated pipelines, unit tests, classroom demonstrations, agricultural comparisons, and travel planning where repeatability is valuable. Save both the original date and latitude with the result so another person can reproduce it. For navigation, safety-critical fieldwork, religious observance, or precise scientific measurement, consult an authoritative local ephemeris that incorporates coordinates, elevation, and current atmospheric assumptions.