What the result tells you
The tool gives four things for the date you enter:
- The phase: one of the eight names, from new moon to waning crescent.
- The lit fraction: the percentage of the disc lit by the Sun, to one decimal.
- The age of the Moon: the number of days since the previous new moon, between 0 and 29.5.
- The full moons since then: for a date in the past, how many full moons have risen from that day until now. At 30 years old you have lived through about 371 of them.
The Moon is drawn with north at the top, as seen from the northern hemisphere. If your device is in the southern hemisphere the picture is flipped, as it is on the calendar pages.
Why the dates 1900 to 2100
The Moon’s motion is one of the best measured in astronomy. The formulas used here keep the Moon’s position within about one arcminute over those two centuries, far better than what the eye can tell on a drawing. Outside that range the tool would still give a plausible answer, but we have not checked it against reference almanacs, so the form stops there.
Dates follow the Gregorian calendar, which every country in the world had adopted for civil use by the 1920s. For a birth registered in the Julian calendar before that, in Russia before 1918 or in Greece before 1923, convert the date first by adding 13 days.
Other dates worth looking up
The tool works for any day, not only birthdays. People use it for a wedding date, the birth of a child, a historic event or the night of an old photograph. The Apollo 11 landing on 20 July 1969 happened under a waxing crescent, six days after new moon: the low Sun at the landing site cast the long shadows that made the craters easy to see.
Questions and answers
What was the Moon phase when I was born?
Enter your date of birth above. The tool computes the angle between the Moon and the Sun on that day and gives the phase, the percentage of the disc that was lit and the number of days since the previous new moon.
Does the time of birth matter?
A little. The Moon moves about 12° a day relative to the Sun, so the lit part changes by up to 12 points of percentage in 24 hours near the quarters, and by much less near new and full moon. Add your time of birth if you want the exact figure. Without it, the tool uses noon Universal Time.
Is the Moon the same phase on every birthday?
No. Twelve lunations last 354 days, so the phase on a given date comes about eleven days earlier in the cycle each year. The phase returns to nearly the same date after nineteen years: you were born under almost the same Moon as on your 19th, 38th and 57th birthdays.
What is the moon phase soulmate trend?
A game that went around TikTok: two people compare the Moon of their birth dates, and if the two lit parts fit together into a full disc, they are said to be made for each other. It is a nice way to look up two Moons. Nothing in astronomy connects it to compatibility.
Does being born on a full moon mean anything?
Not that anyone has measured. Large studies of hospital records find no more births at full moon than on other days, and no link between the phase at birth and character. The phase is still a real fact about the sky on your first night.
Updated November 11, 2026