How to read the phase
The lunar cycle runs about 29.5 days from one new moon to the next, though individual cycles vary by several hours either side of that average. In the first half the lit portion grows (waxing); after the full moon it shrinks (waning). Traditional practice attaches intentions to that rhythm: beginnings and attraction to the waxing half, release and clearing to the waning half. Our guides on candle and moon rituals go through each phase in practical detail.
What the numbers mean
Illumination is the share of the visible disc that is lit; it is close to 0% at the new moon and 100% at the full moon. Days into the cycle (the moon's "age") counts from the exact moment of the most recent new moon, not from a monthly average. The four principal phases are the instants when the Moon and Sun reach particular angular separations, so a phase is really a moment rather than a whole day — the labels in between (crescent and gibbous) cover the days on either side.
Find the moon phase on your birthday
Enter your date of birth in the field above: the calculator works for any date, so it doubles as a birth-moon lookup. The phase you were born under has its own body of lore — the waxing phases are traditionally associated with growth and outward energy, the waning phases with reflection and release — and our ritual guides describe how practitioners use each phase.
Accuracy and limits
The calculation follows Meeus, whose series accounts for the real variation in the Moon's orbit rather than assuming a fixed month; a simple average-month formula can be wrong by as much as seventeen hours, which is enough to put a new moon on the wrong calendar day. The remaining error here is on the order of a minute. Two honest caveats: a phase falling near midnight can land on a different date depending on your time zone, and the date field is read at noon local time, so the phase shown for a past date is the phase at midday.