Lunar Phase Calculator

Select any date to see the moon's phase for that day, from new moon to full moon and all eight phases in between. The calculator shows the illuminated fraction, moon age (days since the last new moon), and upcoming new moon and full moon dates.

The eight lunar phases

Phase	Illumination	Visual description	Typical rise / set (approx.)
🌑 New Moon	0%	Invisible - between Earth and Sun	Rises at sunrise; sets at sunset
🌒 Waxing Crescent	1–49%	Thin sliver on right side	Rises mid-morning; sets before midnight
🌓 First Quarter	50%	Right half lit (northern hemisphere)	Rises at noon; sets at midnight
🌔 Waxing Gibbous	51–99%	More than half lit, right side	Rises mid-afternoon; sets before dawn
🌕 Full Moon	100%	Entire face illuminated	Rises at sunset; sets at sunrise
🌖 Waning Gibbous	99–51%	More than half lit, left side	Rises mid-evening; sets mid-morning
🌗 Last Quarter	50%	Left half lit (northern hemisphere)	Rises at midnight; sets at noon
🌘 Waning Crescent	49–1%	Thin sliver on left side	Rises before dawn; sets mid-afternoon

How the calculation works

The tool uses the Julian Date method (Meeus algorithm), anchored to a known new moon on January 6, 2000. It computes the number of days elapsed since that reference, then takes the modulo of the synodic month (29.53059 days) to find the moon's current age.

Synodic vs. sidereal month

Synodic month (29.53 days): the time from one new moon to the next - the full phase cycle as seen from Earth. This is what lunar calendars and this calculator use.
Sidereal month (27.32 days): the time for the Moon to complete one full orbit relative to the distant stars. It is shorter than the synodic month because Earth also moves along its orbit - the Moon must "catch up" to realign with the Sun.

Moon phase effects

Tidal forces: tides are strongest at new and full moon (when the Sun, Earth, and Moon align), producing spring tides with the highest highs and lowest lows. At first and last quarter, tidal range is reduced (neap tides).
Gardening traditions: biodynamic gardening schedules planting, pruning, and harvesting activities around lunar phases - root crops planted near new moon, above-ground crops near full moon. Scientific evidence is mixed, but the practice remains widespread.
Night sky observation: the full moon washes out faint objects. Astronomers and astrophotographers plan sessions around the new moon for the darkest skies.

Blue moon and supermoon

Blue moon: popularly defined as the second full moon in a calendar month. Because the synodic month (29.53 days) is shorter than most months, this occurs approximately every 2.7 years. Blue moons are not actually blue in color; the phrase originated from a historical meaning of "rare."
Supermoon: a full moon that occurs near perigee - the Moon's closest point to Earth in its elliptical orbit. A supermoon appears approximately 14% larger and 30% brighter than a full moon at apogee (farthest point). There is no universally agreed definition of the distance threshold, so the number of supermoons per year varies by source (typically 3–4).