Moon phase calculator
Pick a date, get the moon phase and the next full moon.
How is the moon phase calculated?
With the method in Jean Meeus’s Astronomical Algorithms: the mean lunar cycle of 29.530589 days, corrected by dozens of periodic terms for the eccentric orbits of the Moon and Earth and small planetary effects. That gives the true moments of new moon, first quarter, full moon and last quarter to within about a minute of the times published by the US Naval Observatory. The share of the disk that is lit comes from the Sun–Moon angle.
When is the next full moon?
Pick today’s date above: the result lists the next new moon, first quarter, full moon and last quarter with the exact time in your time zone and in UTC. Full moons come about every 29.5 days, so the date can differ by a day between the East and West Coasts.
What do waxing, waning, crescent and gibbous mean?
Waxing means the lit part is growing (from new moon to full), waning that it is shrinking. A crescent is less than half lit, gibbous more than half. The calculator names the day by the main phase that falls on that date in your time zone; on other days it shows the in-between phase.
What is the moon’s age?
The number of days since the last new moon. A lunar month averages 29.53 days but runs from about 29.3 to 29.8 days, and full moon comes at an age of anywhere from about 13.9 to 15.6 days — which is why simple “average cycle” calculators can be off by half a day or more.
Why does the date of a full moon depend on where I am?
The phase happens at one instant for the whole Earth, but clocks differ. A full moon at 04:12 UTC falls on one date in New York and on the evening before in California. The calculator shows times in your device’s time zone and in UTC.
What are the eight phases of the moon?
In order: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last (third) quarter and waning crescent. The four named moments (new, first quarter, full, last quarter) are instants; the four in-between names are periods of about a week. At the two quarters exactly half of the disk that faces Earth is lit.
Why is the lunar month 29.5 days when the moon orbits in 27.3?
The 27.3-day figure is the time the moon takes to circle the Earth against the stars. In that time the Earth has moved about a twelfth of the way round the Sun, so the moon needs roughly two more days to line up with the Sun again. The phase cycle, the synodic month, is therefore about 29.5 days.
Does the moon look the same everywhere on Earth?
The phase and the percent lit are the same, but the orientation is not. In the Northern Hemisphere a waxing moon is lit on the right; in the Southern Hemisphere it is lit on the left, and the crescent seems to lie on its back near the equator. The picture in the result shows the northern view.
Worked example
For noon UTC on November 1, 2026 the calculator gives a moon that is 54% lit, waning, 21.8 days old, named waning gibbous. The next main phases follow at last quarter in 0.4 days, new moon in 7.8 days, first quarter in 16 days, full moon in 23.1 days. The gaps between main phases average about 7.4 days (a quarter of 29.53) but are not equal, because the moon's orbit is an ellipse and it moves faster when it is nearer the Earth.
How to read the result
Illumination is the fraction of the visible disk that is lit, from 0% at new moon to 100% at full moon. It follows the Sun–Moon angle, so it changes slowly near new and full moon and fastest at the quarters, and it is not a straight line in time: a moon at age 7 days is about half lit, not about a quarter. The age is counted from the last true new moon, not from a fixed 29.53-day average, which is why it can reach nearly 30 days at the end of a long month.
Common mistakes
Mixing up local time and UTC is the usual cause of a full moon appearing a day off against another calendar. Another is assuming the quarter moon is “a quarter lit”: it is named for a quarter of the orbit and is half lit. Third, a new moon is not visible in the sky and has nothing to do with the dark side of the moon; the far side is lit as often as the near side.
Related: sunrise and sunset calculator, sun angle calculator, time zone converter.
Sources: Jean Meeus, Astronomical Algorithms, 2nd ed., chapters 48–49; NASA Goddard, polynomial expressions for Delta T (Espenak and Meeus); checked against the US Naval Observatory’s Phases of the Moon for 2026. How we check our calculators.