Find the moon phase you were born under
One date, no birth time: the phase you were born under and exactly how much of the Moon was lit.
How we calculate it
Everything starts from one angle, the elongation: how far the Moon has moved ahead of the Sun along the ecliptic, from 0° at new moon through 180° at full moon and on to 360°. We compute both positions with Jean Meeus’s astronomical algorithms, for 12:00 UTC on your date.
The lit share follows from that angle: (1 − cos elongation) / 2. It is a cosine, not a straight line, so the percentage changes fastest around the quarters and barely moves around new and full moon. Observatories publish the same figure.
Sites draw the borders between phases differently. We cut the cycle into eight equal segments of about 3.7 days, each centered on the exact moment of its phase, the same split the TikTok moon phase trend uses. NASA names only the exact moments and calls the days in between waxing or waning crescents and gibbous moons, so a date one day after new moon reads “new moon” here and “waxing crescent” there. The percentage lit is the same on both sites.
An example: on 8 March 1990 at noon UTC the Moon was 145.24° from the Sun. (1 − cos 145.24°) / 2 = 0.91, so 91% of the disc was lit; the Moon was 11.9 days into its 29.5-day cycle, inside the segment centered on 135°: waxing gibbous.
Reading the date at noon UTC means you never need a birth time: whatever the hour, the lit share is off by 5.8 points at most. The name is less forgiving near a border, so when it changes within twelve hours either side of that noon, the result shows the exact time, in UTC, when one phase hands over to the next; that happens on about one date in four.
The eight phases at a glance
New Moon
Under 4% lit. Starts on instinct, before any plan exists.
Waxing Crescent
4–31% lit, waxing. Grows by pushing against the way things were.
First Quarter
31–69% lit, waxing. Decides under pressure and builds the frame.
Waxing Gibbous
69–96% lit, waxing. Refines, questions and closes the last gaps.
Full Moon
96–100% lit. Sees both sides and learns most through other people.
Waning Gibbous
96–69% lit, waning. Explains what worked and passes it on.
Last Quarter
69–31% lit, waning. Ends what has outlived its use.
Waning Crescent
31–4% lit, waning. Wraps up the cycle and lets go early.
Opposite moon phases
Every phase has an opposite about 14.8 days away, and at their exact moments the two lit parts together make one full disc.
- New MoonFull Moon
- Waxing CrescentWaning Gibbous
- First QuarterLast Quarter
- Waxing GibbousWaning Crescent
Don’t confuse it with your Moon sign
The phase is about light: how far the Moon stood from the Sun, and how much of its disc that separation left lit. The Moon sign is about position: the stretch of the zodiac the Moon was crossing, a separate calculation with its own readings. Your date always settles the phase; the sign changes every two days or so, and on a changeover day only the birth time decides it.
Find your Moon signBirth moon phase questions
What moon phase was I born under?
Type your birth date into the calculator above: it works out the Moon’s angle from the Sun at noon UTC that day and names the phase from it. There are eight phases, and each takes up about 3.7 days of the 29.5-day cycle.
How do I find the moon phase on my birthday without the time?
You don’t need the time: the date alone is enough. Over a whole day the lit share moves by 11.6 percentage points at most, and a random hour of birth gives a different name from our noon reading only about 7 times in 100, and then only the neighboring phase.
Is the birth moon phase the same as my Moon sign?
No. The phase is the lit share of the Moon’s face; the Moon sign is the zodiac sign the Moon occupied. Two people born under the same phase can have Moon signs far apart, and the sign sometimes needs a birth time, while the phase never does.
Does the birth moon phase mean anything in astrology?
Yes. Western astrology reads the Sun–Moon angle at birth as a lunation type, an approach Dane Rudhyar laid out as eight types in the twentieth century. The couple version has no such history: comparing two people’s phases comes from a TikTok trend.
What is the rarest moon phase to be born under?
None by a margin that matters. Across 31,673 dates from 1940 to 2026, new moon and full moon take 12.2% each and first quarter the most, 12.8%: around new and full moon the Moon moves slightly faster, so those windows pass a little sooner.
Why does NASA call my date a different phase?
Because NASA keeps its own names for four instants (new moon, first quarter, full moon and last quarter) and describes the rest of the month by shape: crescent or gibbous, waxing or waning. Both sites print the same percentage lit; only the label differs.