Moon Phase Calculator - Phase, Illumination, Age & Next Full Moon
Moon Phase Calculator
See the Moon's phase for any date and when the next full moon is
Phase at a Glance
A picture of the Moon, its name, how much is lit and how old it is.
The Next Four Phases
Dates and times of the next new moon, first quarter, full moon and last quarter.
Either Hemisphere
The Moon looks mirrored in the southern hemisphere; pick your view.
Full Privacy
Everything is calculated in your browser.
How the Moon's Phase Is Worked Out
The phase depends on the angle between the Sun and the Moon as seen from the Earth. The tool computes the ecliptic longitude of each, using a truncated version of Jean Meeus's lunar series for the Moon, and takes the difference: 0° is a new moon, 90° first quarter, 180° a full moon and 270° last quarter. The illuminated fraction is (1 − cos of that angle) ÷ 2, and the dates of the next phases come from finding when the angle reaches each target.
Phase times are accurate to a few minutes and the illuminated percentage to well under one percent. The Moon's age is the time since the last new moon, which varies from about 29.3 to 29.8 days between cycles, so the average of 29.53 days is only a guide. The times shown use your device's time zone, and the names of the eight phases cover 45° of the cycle each, so "New Moon" and "Full Moon" describe the day or so around the exact moment.
Key Takeaways
- Any date 1800 to 2200: Look back at a birthday or ahead to an event.
- Waxing or waning: Tells you whether the Moon is getting fuller or thinner.
- Minutes-level phases: Phase times are good to a few minutes.