Moon Phases
The Eight Faces of the Moon
The Moon takes about twenty-nine and a half days to travel from dark to full and back again. Each stage of that journey has its own character — and one of them was hanging above you on the day you were born.
How we work out your moon phase
Every number on this site comes from a professional astronomical calculation, not an estimate. We use the same class of mathematics astronomers use to predict eclipses, and we check our results two independent ways before we publish them. Here is exactly how it works, and why our answer might differ slightly from another website's.
A birthday is a day, but the Moon keeps moving
The Moon travels roughly twelve degrees across the sky every twenty-four hours. That means the phase at one minute past midnight is genuinely different from the phase at midnight the following night — sometimes different enough to cross from one named phase into the next.
Since a birth date carries no time of day, we calculate for midday — 12:00 UTC — on the date you enter. It is the fairest single choice available: it keeps the answer as close to correct as possible no matter where in the world you were born, because the worst it can ever be out is twelve hours rather than twenty-four.
If another site gives you a slightly different phase, this is almost always the reason. Many of them quietly calculate for midnight, or for their own server's timezone, without telling you.
When we call a Moon 'New' or 'Full'
A New Moon, First Quarter, Full Moon and Last Quarter are single instants, not days. So every site has to decide how wide a window around that instant still counts.
The common shortcut is to divide the cycle into eight equal slices. It is simple, and it is wrong in a way you can see with your own eyes: it labels roughly one day in eight a 'New Moon', including evenings when a clearly visible crescent is hanging in the sky.
We use a tighter rule. If your birth date falls within twelve hours of the exact moment of a New Moon, First Quarter, Full Moon or Last Quarter, we name that phase. Otherwise we name the crescent or gibbous phase you would actually have seen. It means roughly one day in thirty is a New Moon — which matches what the sky was really doing.
How we know the numbers are right
Getting this wrong would be easy and invisible, so we check it two ways that do not depend on each other.
First, we calculate every New and Full Moon between 1905 and 2025 a second time, using a completely separate method published by the astronomer Jean Meeus. The two calculations agree to within three minutes across the whole period, with no drift in either direction.
Second, we check against events that cannot be argued with. A total solar eclipse can only happen at a New Moon, and a total lunar eclipse only at a Full Moon. We test eleven real eclipses between 1999 and 2024, and every one lands on the phase it must.
These checks run automatically every time we change the site, so they cannot quietly stop being true.
What we can and cannot tell you
We can tell you, accurately, the day of the week you were born and what the Moon was doing above you. That part is astronomy and it is verifiable.
What those things mean is a different kind of knowledge. The readings on this site draw on long traditions of lunar and day-of-week symbolism, and they are offered for reflection rather than prediction. Nothing here is medical, psychological, financial or legal advice, and nothing here is a forecast of what will happen to you.
Read them as a mirror rather than a map.