Moon Phase Calculator
Find the moon phase for any date
Thursday, 9 July 2026
Waning Crescent
28% illuminated
Next full moonWednesday, 29 July 2026
Next new moonTuesday, 14 July 2026
How it works
The Moon does not produce its own light — we see it because sunlight reflects off its surface. As the Moon orbits Earth, the angle between the Sun, Earth, and Moon changes, so the portion of the lit side we can see from Earth changes too. One complete cycle from new moon to new moon takes about 29.5 days, which is why moon phases follow a predictable monthly rhythm.
This calculator uses a standard astronomical approximation: a known new moon at 18:14 UTC on 6 January 2000 as a reference point, plus a synodic month of 29.53058867 days. For any date, it works out how many days have elapsed since that reference, divides by the cycle length, and finds the position within the current cycle. From that position it derives the illumination percentage, phase name, and estimated days until the next full and new moons — no API or telescope required.
Moon phases have long been used as a practical calendar in farming, fishing, and navigation, and they still influence coastal tides (alongside the Sun). Many cultures mark lunar festivals and folklore around the full moon. This tool gives a quick mathematical snapshot; for precise astronomical times to the minute, observatories use orbital models that account for the Moon's elliptical path.
Frequently asked questions
How often does a full moon occur?
Full moons occur once per synodic month — about every 29.5 days. That works out to roughly 12 full moons a year, with an occasional 13th (a “blue moon” in the seasonal sense) when the timing of the cycle aligns that way. The exact date and time shift slightly each month because the Moon's orbit is not a perfect circle.
Is the moon phase the same everywhere on Earth?
Yes — at any given moment, everyone on Earth sees the same moon phase. Someone in London and someone in Sydney both see a waxing gibbous (or whatever the phase is) at the same universal time. What changes by location is when the Moon rises and sets, and which way up it appears in the sky — not which fraction of the disc is lit.
How are moon phases calculated?
Clockr uses a synodic month of 29.53058867 days and a reference new moon at 18:14 UTC on 6 January 2000. Days since that reference are divided by the cycle length; the remainder is the Moon's age in the current cycle. Illumination comes from a cosine of that age, and the eight named phases are assigned by dividing the cycle into equal eighths.
How long is a lunar cycle?
A synodic month — the time from one new moon to the next — averages about 29.53 days (29 days, 12 hours, and 44 minutes). That is slightly longer than the Moon's orbital period around Earth because Earth is also moving around the Sun, so the Sun–Moon angle takes longer to repeat.