Moon phase on my birthday

Enter your birthday to see the moon on the day you were born: its shape, how much was lit, and when your birthday next falls on a full moon.

Why the moon has phases

The moon doesn’t make its own light. Half of it is always lit by the Sun, and as it travels around the Earth, about once every 29.5 days, we see different amounts of that lit half. When the moon is between us and the Sun, its lit side faces away from us: a new moon. When it’s on the far side of the Earth from the Sun, we see the whole lit face: a full moon. In between, the lit part grows (waxes) for about two weeks, then shrinks (wanes).

How it’s worked out

The times of every new moon, quarter and full moon are calculated with the standard method in Jean Meeus’s Astronomical Algorithms (1998), a standard reference in astronomy. We checked it against NASA’s catalog of moon phases: more than 2,000 phases from 1601 to 2100 match to the minute.

The page shows the moon at midday in your own time zone. The four main phases are named only on the day they happen, and the days between get in-between names. Because the moon changes a little every hour, and what you’d have seen depends on where you were born, the result is accurate to within about a day.

Seen from the Southern Hemisphere

From south of the equator, the moon looks upside down compared with how it looks from the north, so a waxing moon is lit on the left instead of the right. Turn on “Southern Hemisphere view” to flip the drawing and the image. Near the equator, a crescent tends to lie on its side, like a bowl.

Your next birthday with a full moon

Full moons come round every 29.5 days, so they drift through the calendar from year to year. A birthday often lines up with the same phase again after 19 years, because 19 years is almost exactly 235 lunar months, though a few hours’ difference can move it by a day.

Old dates and the calendar change

The Gregorian calendar began in October 1582, and countries adopted it at different times. Britain and its colonies, including those in North America, switched in September 1752, when 11 days were skipped. Dates on this page are in the Gregorian calendar, so for someone born before their country switched, the date written down at the time may be different.

What’s saved

If you choose to remember your birthday, it’s saved in your browser so the birthday tools can use it, and your hemisphere choice is saved the same way. Neither is ever sent to us.

The eight phases of the moon

New moon: The moon sits between the Earth and the Sun, so its lit side faces away from us. It rises and sets with the Sun and can’t be seen.
Waxing crescent: A thin curve of light that grows each evening. It’s seen in the west after sunset and sets a few hours later.
First quarter: Half the moon is lit. It rises around midday, is high at sunset, and sets around midnight.
Waxing gibbous: More than half lit, and growing. It rises in the afternoon and lights most of the evening.
Full moon: The whole face is lit. It rises around sunset and sets around sunrise, so it’s up all night.
Waning gibbous: Still more than half lit, now shrinking. It rises after dark and is still up in the morning.
Last quarter: Half lit again, the other half this time. It rises around midnight and is still high in the morning sky.
Waning crescent: A thin curve rising in the east before dawn, shrinking each morning until the next new moon.