About this tool
This moon phase calculator tells you what the moon looks like on any date, past or future. Pick a date and it shows the phase name (New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Last Quarter, or Waning Crescent), the percentage of the disc that is lit, the moon's age in days since the last new moon, and a drawing of the moon as it appears from the Northern Hemisphere. Below that you get the exact dates and times of the next new moon, first quarter, full moon, and last quarter in your own time zone, plus a table of every full moon in the year with its traditional name (Wolf Moon, Harvest Moon, and so on). It is useful for planning night photography, fishing and hunting trips, gardening by the moon, stargazing away from a bright moon, or simply checking whether tonight's moon is full.
How it works
Phase times use the mean-phase formula from Jean Meeus's Astronomical Algorithms (chapter 49): JDE = 2451550.09766 + 29.530588861·k, where k counts lunations from the new moon of 6 January 2000 and quarter phases use k + 0.25, 0.5, and 0.75. To that mean time the calculator adds the full set of periodic corrections for the Sun's and Moon's anomalies, the Moon's argument of latitude, and the 14 planetary terms, which brings the result to within a few minutes of the published almanac value (the tiny difference between Dynamical Time and UTC, about one minute, is ignored, so treat times as accurate to roughly ±1 hour in the worst case). The moon's age is the time since the most recent computed new moon, and the illuminated fraction is (1 − cos(2π·age ÷ 29.530588853)) ÷ 2, a good approximation that ignores the small effect of the Moon's orbital eccentricity. As a cross-check the code also carries the simple mean cycle counted from the reference new moon at JD 2451550.1 (2000-01-06 18:14 UTC).
Frequently asked questions
How accurate are the phase times?
The Meeus algorithm with its full periodic corrections gives new, quarter, and full moon instants to within a few minutes of values published by the US Naval Observatory or NASA. The times here are shown in your browser's time zone, so a full moon that falls late at night may appear on a different calendar date than it does for someone in Asia or Europe.
What does the moon's age mean?
The age is the number of days since the last new moon. A complete cycle (one synodic month) averages 29.53 days, so first quarter arrives around day 7.4, full moon around day 14.8, and last quarter around day 22.1. Because the Moon's orbit is elliptical, the real intervals between phases vary by more than a day, which is why this page computes the actual instants instead of assuming equal quarters.
Why is the illumination not exactly 50% at first quarter?
At the moment of first or last quarter the Moon is geometrically half lit as seen from Earth, so the exact figure is 50%. This page evaluates the phase at noon on the chosen date, not at the exact quarter instant, so you will usually see a number a few percent either side of 50. The illumination figure is a smooth approximation good to about one percentage point.
Where do the full moon names come from?
The names used here (Wolf, Snow, Worm, Pink, Flower, Strawberry, Buck, Sturgeon, Corn or Harvest, Hunter's, Beaver, Cold) are the ones popularized by the Old Farmer's Almanac, drawn from Algonquian and colonial American traditions. Strictly, the Harvest Moon is the full moon nearest the September equinox, so in some years it falls in early October. When a month has two full moons the second is commonly called a Blue Moon.