Day Length Calculator

How to Use the Day Length Calculator

1. 1. Choose the place. Pick a city to fill in its coordinates and time zone, or type your own latitude and longitude in decimal degrees (north and east positive). Use my location asks your browser for your position and uses it on this page only.
2. 2. Pick a date. The calculator opens on today's date in the chosen time zone. Any year works, and the chart below redraws for the year you pick.
3. 3. Read the day. The headline is the length of the day in hours and minutes. Sunrise, sunset and solar noon are shown as clock times in your chosen zone, with a note when one falls on the next or previous calendar day, and the last box shows the change since the day before.
4. 4. Read the year. The longest and shortest days of the year, and the number of days of midnight sun and polar night if there are any, sit above a chart of daylight hours with your date marked.

What Counts as Daylight

Day length here is the time from sunrise to sunset, and both are defined by the Sun's centre reaching 0.833° below the horizontal. That figure adds the Sun's apparent radius, about 0.27°, to 0.57° of standard atmospheric refraction, so sunrise is the moment the upper edge of the Sun first appears and sunset the moment it disappears. Twilight is extra: civil twilight lasts until the Sun is 6° down, nautical until 12° and astronomical until 18°. The times come from the NOAA solar algorithm, based on Jean Meeus's Astronomical Algorithms, which NOAA states is accurate to within a minute between 72° north and south and within ten minutes beyond.

Why Day Length Changes With Latitude and Season

Earth's axis is tilted about 23.4° to its orbit, so the latitude where the Sun is overhead, the declination, swings between −23.4° and +23.4° through the year. In your hemisphere's summer the Sun's daily arc is longer and higher, so days are long; in winter the arc is short and low. The closer you are to the equator, the less this matters. Away from the extremes the day changes fastest around the equinoxes: in New York on 20 March 2026 the day gains 2 min 43 s over the day before, while in Reykjavik it gains 6 min 32 s.

Singapore, a degree and a bit from the equator, hardly changes at all, and Quito stays within a minute of 12 h 7 min all year. Sydney's seasons are reversed: its longest day is in December. The equinox day is not exactly 12 hours either. Because sunrise is measured at the Sun's upper edge and refraction lifts the Sun into view early, New York has 12 h 9 min of daylight on 20 March, and the day is closest to 12 hours (the equilux) on 17 March.

Polar Day and Polar Night

Beyond roughly 66.6° the day length leaves the 0 to 24 hour range: for part of the year the Sun never sets, and for part it never rises. The calculator reports these as polar day and polar night and counts them. At Tromsø, Norway, it finds the Sun up all day on 69 days of 2026 and never up on 48 days. Local figures for the midnight sun differ by a few days from these, because they depend on the horizon convention, hills and whether twilight is counted.

Accuracy and Limits

• Terrain and altitude are not modelled. A mountain to the west cuts the observed day short; a viewpoint above sea level lengthens it.
• Weather and refraction change the visible times by a minute or more, especially at high latitudes where the Sun grazes the horizon.
• Daylight saving time affects the clock times shown, never the length of the day.
• Earliest sunrise and latest sunset do not fall on the solstice. The equation of time shifts solar noon through the year, so in mid-latitudes the earliest sunrise of the year comes about a week before the longest day and the latest sunset about a week after it.

Frequently Asked Questions

How do you calculate the length of the day?

Find the Sun's declination for the date, then solve for the hour angle at which the Sun's centre is 0.833° below the horizon: cos H = (cos 90.833° ÷ (cos φ cos δ)) − tan φ tan δ. Daylight is 2H divided by 15, in hours. Latitude φ and declination δ are the only inputs that matter, which is why longitude and time zone change the clock times but not the length.

How many hours of daylight does my city get on the longest day?

It depends on latitude. At the equator it is about 12 h 7 min, at Cairo's 30° north it is about 14 h, at New York's 41° about 15 h, in London about 16.6 h and at Reykjavik's 64° about 21 h. Above the Arctic Circle it reaches 24 hours.

Why is the equinox not exactly 12 hours of daylight?

Sunrise and sunset are measured when the Sun's upper edge meets the horizon, and refraction lifts the Sun into view while it is still geometrically below it. Both effects add a few minutes. At mid-latitudes the day is closest to 12 hours a few days before the spring equinox and a few days after the autumn one.

Why do the days get longer fastest in March and September?

Around the equinoxes the Sun's declination changes fastest, about 0.4° a day, so the Sun's daily arc lengthens or shortens most quickly. Near the solstices the declination barely moves, which is why the day length is almost flat for a few weeks around 21 June and 21 December.

Which places get the midnight sun?

Anywhere north of the Arctic Circle (about 66.56° N) has at least one day of continuous daylight, and anywhere south of the Antarctic Circle has one in the southern summer. Tromsø in Norway, Murmansk in Russia, Utqiagvik in Alaska and Iceland's island of Grímsey are well known examples. Reykjavik, at 64° N, never quite gets one, but its June nights are twilight all the way through.

Does daylight saving time change how long the day is?

No. Daylight saving moves the clock times of sunrise and sunset by an hour, but the number of hours between them is set by the Sun alone. The calculator shows clock times in the time zone you choose, with daylight saving applied for that date.