Moon Phase Calculator (any date, illumination %)
Pick a date and get the moon's phase (new, waxing crescent, first quarter, waxing gibbous, full, etc.), age in days, illumination percentage, plus the next new moon and full moon dates.
- Moon age
- 20.3 days
- Phase angle
- 247.5°
- Next new moon
- May 16, 2026
- Next full moon
- May 30, 2026
How it works
How moon phases work
The moon orbits Earth every ~29.53 days (the 'synodic month'). What we see is sunlight reflected off the moon's surface; the visible portion changes as the moon moves around Earth.
Eight standard phases mark the progression: new moon (no illumination), waxing crescent, first quarter (50% illuminated), waxing gibbous, full moon (100%), waning gibbous, last quarter (50% illuminated, opposite side), waning crescent. The cycle repeats.
What 'moon age' means
Moon age is the number of days since the most recent new moon. New moon = age 0. Full moon = age ~14.77 (half of 29.53). The cycle ends and a new one begins when age reaches 29.53.
Used in: lunar calendars (Chinese, Hebrew, Islamic), astronomy timing, photography (specific phases for moonlight intensity), agricultural traditions (planting by phase).
Common uses
Astronomy: full moon makes deep-sky observation difficult (sky too bright). New moon is best for seeing faint nebulas, galaxies, and meteor showers.
Photography: full moon for landscape moonscapes; new moon for stars and Milky Way. Crescent phases produce dramatic Earth-shine images (the dark side of the moon faintly lit by Earth's reflected sunlight).
Tides: high tides peak at new and full moon (when sun and moon align). Lower tides at first and last quarter.
Cultural events: many festivals tied to moon phases. Tsukimi (月見) in Japan watches the harvest moon. Mid-Autumn Festival in China aligns with the September/October full moon.
Frequently asked questions
›How accurate is this?
Within a day for typical years. Uses the average synodic month (29.53 days) and a known new moon reference. Real lunar timing varies by ±15 minutes due to orbital irregularities.
›Why is the moon visible during the day sometimes?
The moon is up roughly half the day, sun-up or sun-down. During waxing and waning phases, the moon and sun are partway apart in the sky — moon is visible during late afternoon (waxing) or early morning (waning).
›What's a 'blue moon'?
A second full moon in the same calendar month. Happens roughly every 2.5-3 years. Doesn't actually look blue; the name comes from the rare-event idiom.
›What's a 'supermoon'?
A full moon at perigee (moon's closest approach to Earth). Looks ~14% larger and 30% brighter than average. Several per year.
›Does the calculator account for hemisphere?
The phase percentage is the same everywhere on Earth, but visual appearance flips between northern and southern hemispheres. Our emoji shows the northern hemisphere view.
›What's the lunar 'sidereal' month?
27.3 days — time for the moon to return to the same position relative to stars. Different from the synodic month (29.5) we use here, which measures phases as seen from Earth.
›Can I use this for past/future centuries?
Yes. Calculation works across millennia, though precision degrades slightly (the synodic month varies by tiny amounts over centuries).
›Does the data leave my browser?
No. Calculation runs locally; nothing is sent to a server.
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