Moon Phase Calculator

Find the approximate moon phase for any date, based on the moon's roughly 29.53-day cycle.

Moon Phase Calculator

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Date

Moon phase

Enter a date

Illumination (approx.)

An estimate based on the average lunar cycle - exact phase times can vary by a few hours.

How this is estimated

Phase = (days since a known new moon) mod (29.53-day lunar cycle)

Example

July 19, 2026 falls at roughly 16% through the cycle from the nearest reference new moon, landing in the Waxing Crescent phase with about 23% illumination.

Step-by-step guide

Enter any date, past or future.
Read the estimated moon phase and approximate illumination percentage.

Common mistakes

Treating this as precise to the hour - the real lunar cycle varies slightly (between about 29.18 and 29.93 days) due to the moon's elliptical orbit, so this average-based estimate can be off by up to a day near phase boundaries.

Assuming the moon phase looks identical everywhere on Earth at the same moment - the visible phase is the same globally, but local moonrise and moonset times differ by location.

Frequently asked questions

How accurate is this estimate?

It's generally accurate to within about a day, since it uses the average lunar cycle length rather than precise astronomical calculations that account for orbital variations. For precise phase timing (like for photography planning), a dedicated astronomy source is more exact.

What are the 8 moon phases?

New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Last Quarter, and Waning Crescent - the moon cycles through all eight roughly every 29.5 days.

Does the moon phase affect tides?

Yes - tides are generally stronger (called spring tides) around new and full moons, when the sun and moon's gravitational pull align, and weaker (neap tides) around the quarter phases.

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