Moon Phase Calculator
Find the Moon’s phase for any date and time in your time zone: the illuminated percentage, the Moon’s age, which side is lit, its distance and zodiac sign, the next new, quarter and full moons, and a day-by-day moon calendar for the month — using Meeus’s astronomical algorithms.
How it works
principal phases = mean lunation (2451550.09766 + 29.530588861 × k Julian days) + periodic corrections (Meeus, ch. 49) − ΔT · Moon age = moment − last new moon · phase angle i = 180° − D − 6.289° sin M′ + 2.1° sin M − 1.274° sin(2D − M′) − 0.658° sin 2D − 0.214° sin 2M′ − 0.11° sin D · illuminated fraction = (1 + cos i) ÷ 2
The Moon’s phase is set by the angle between the Sun and the Moon as seen from Earth. Instead of assuming every cycle lasts an average 29.53 days, this calculator finds the real instants of new moon, first quarter, full moon and last quarter with Jean Meeus’s lunar phase algorithm, which corrects the mean cycle for the pull of the Sun and the Moon’s elliptical orbit and agrees with the US Naval Observatory to within a minute or two for modern dates. The Moon’s age is the time since the last new moon. The lit percentage comes from the phase angle, worked out from the Moon’s and Sun’s positions at the moment you choose, and the Moon’s distance and ecliptic longitude come from the main terms of Meeus’s lunar theory. A calendar day is named after one of the four main phases when that phase happens on that day in your time zone; other days are waxing or waning crescents and gibbous moons. You also get which side of the Moon looks lit from your hemisphere, the next phases with their local times, and a day-by-day moon calendar for the month.
Worked example
For October 19, 2026 at 12:00 noon in US Eastern time (UTC−4), the last new moon was on October 10 at 11:50 AM, so the Moon is 9.0 days old. First quarter fell the day before, on October 18 at 12:13 PM, so October 19 is a Waxing Gibbous day with about 60% of the disc lit — the right-hand side from the Northern Hemisphere. The next full moon is October 26 at 12:12 AM, in 7 days, and the next new moon is November 9 at 2:02 AM. The Moon is about 400,000 km away, in Aquarius.
Sources: Jean Meeus, Astronomical Algorithms (2nd ed.), ch. 47–49 · US Naval Observatory — Phases of the Moon · Lunar phase — Wikipedia
Frequently asked questions
How accurate is this moon phase calculator?
The four main phases are timed with Meeus’s full correction series, which matches the US Naval Observatory to about a minute between 1900 and 2100, and the lit percentage is within about half a percentage point. The old shortcut of adding 29.53-day cycles can be wrong by up to 14 hours, because individual cycles run from about 29.3 to 29.8 days.
What do the eight moon phases mean?
New moon (the Moon is between Earth and Sun, unlit), waxing crescent, first quarter (half lit, growing), waxing gibbous, full moon (opposite the Sun, fully lit), waning gibbous, last quarter (half lit, shrinking) and waning crescent. The four main ones are exact instants; the other four are the stretches between them.
Why does the full moon date differ between websites?
A full moon is a single moment worldwide, so its calendar date depends on the time zone. A full moon at 1:28 AM in London is still the evening before in New York. Pick your zone to see the date and time where you are.
What is the Moon’s age?
The time since the last new moon, in days. It runs from 0 to about 29.5: roughly 7.4 at first quarter, 14.8 at full moon and 22.1 at last quarter, though each value shifts by several hours from cycle to cycle.
Which side of the Moon is lit?
In the Northern Hemisphere a waxing Moon is lit on the right and a waning Moon on the left; in the Southern Hemisphere it is the other way round. Near the equator the crescent lies more on its back, lit from below or above.
How do I find the moon phase on the day I was born?
Enter your birth date, choose the time zone you were born in and, if you know it, the time of birth under More options. The calculator shows the phase, lit percentage and age at that moment, and the month calendar shows the days around it.
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This calculator is for educational purposes. Double-check important results before acting on them.