🌙 Moon Phase Calculator
Pick a date to see the moon phase — its name, how illuminated it is, its age in days, and when the next full and new moon fall.
Waxing Crescent
Illumination
16%
Moon age
3.9 days
Next full / new
11d / 26d
The moon cycles through its phases every 29.53 days (the synodic month). Illumination is the lit fraction of the disc you see. Computed from the mean synodic period anchored to a known new moon — accurate to within a few hours, which is plenty for the phase. 🔒 In your browser.
How the moon phase calculator works
The moon cycles through its phases every 29.53 days — the synodic month, the time from one new moon to the next. The tool measures how far through the current cycle the chosen date is (the moon's "age" in days), anchored to a known reference new moon, and from that gives the phase name and the illuminated fraction of the disc.
This uses the mean synodic period, so it's accurate to within a few hours — more than enough to identify the phase and plan around a full or new moon. The exact instant of each phase wobbles slightly because the moon's orbit isn't a perfect circle.
Frequently asked questions
What moon phase is it today?
Set the date to today and the tool shows the current phase, its illumination and the moon's age in days. The eight phases run new → waxing crescent → first quarter → waxing gibbous → full → waning gibbous → last quarter → waning crescent.
How long is the moon's cycle?
29.53 days — the synodic month, from one new moon to the next. That's why full moons fall on different calendar dates each month and there's occasionally a second full moon (a "blue moon").
What does moon illumination percentage mean?
The fraction of the moon's disc that's lit as seen from Earth. 0% is a new moon (dark), 50% is a quarter moon (half lit), and 100% is a full moon. It rises and falls smoothly through the cycle.
When is the next full moon?
The tool shows the days until the next full and new moon from your chosen date. Full moons recur about every 29.5 days.
What is the moon's age?
How many days it's been since the last new moon — 0 at new moon, about 7.4 at first quarter, 14.8 at full, and 22 at last quarter, resetting after 29.53 days.