Birthday Moon Phase Calculator

What does a birth moon phase result show?

The result card gives you six separate pieces of information, from the phase name to a note about phase changes.

• Phase name: one of eight, each covering a 45° slice of the Moon’s monthly cycle.
• Percent lit: the share of the Moon’s face the Sun lit, as seen from Earth. A New Moon is close to 0%, a Quarter Moon about 50% and a Full Moon close to 100%.
• Days since the New Moon: the Moon’s age on your birthday, out of an average cycle of 29.5 days. The catch is that it’s an estimate. The Moon speeds up and slows down along its orbit, so the figure can be off by up to about half a day.
• Degrees ahead of the Sun: the angle between the Sun and the Moon along the sky’s path. 0° is a New Moon, 90° a First Quarter, 180° a Full Moon and 270° a Last Quarter.
• Day before and day after: the phase a day earlier and a day later, marked as the same or different. A different phase means you were born within about a day of a change.
• Change note: if the Moon crossed from one phase to another during your birth date, the card names both phases.

How do I share or save my result?

Use Share, Save image or Copy link to turn your result into a link or a portrait picture, 1080 × 1350 pixels. Thing is, the link carries your birth date after the # sign, so anyone you send it to can read the date. Browsers don’t send that part to a server, and the tool saves nothing in cookies or local storage. Share the link only with people you’re happy to have your date.

Use the Northern sky and Southern sky switch to match the Moon’s lit side to where you live.

What are the eight birth moon phases?

The Moon moves through eight phases, each a 45° slice of its roughly 29.5-day cycle, so each one covers about one in eight birthdays. None is rare. Find yours in the table, then read its entry below.

The lit side flips in the Southern Hemisphere. Rise and set times in the entries are rough, because they move with your latitude and the season.

What does a New Moon birth phase mean?

A New Moon birthday falls within about 1.8 days of the exact New Moon, with 0 to 3.8% of the Moon lit. The Moon sat almost in line with the Sun, so the side facing Earth was dark. It rose and set close to the Sun’s times, which is why nobody could see it on your birthday.

Lunar astrology links the New Moon with beginnings, instinct and privacy. It describes New Moon people as quiet starters who trust a feeling before they can explain it. Soulmate phase: Full Moon (see New Moon and Full Moon compatibility).

What does a Waxing Crescent birth phase mean?

A Waxing Crescent birthday falls 1.8 to 5.5 days after the New Moon, with 3.8 to 30.9% lit. The Moon was a thin crescent, lit on the right in the Northern Hemisphere and wider each night. It set some hours after the Sun, so it showed up in the western sky in the evening.

Lunar astrology reads it as emerging and determined, something small that’s sure it will grow. Waxing Crescent people are often described as persistent and still finding their footing. Soulmate phase: Waning Gibbous (see Waning Gibbous and Waxing Crescent compatibility).

What does a First Quarter birth phase mean?

A First Quarter birthday falls 5.5 to 9.2 days after the New Moon, with 30.9 to 69.1% lit. About half the Moon was lit, the right half in the Northern Hemisphere. It rose around midday and stood high in the sky at sunset, so you could often see it in the afternoon.

Lunar astrology links it with action, decisions and meeting challenges head on. First Quarter people are described as quick to decide and unafraid of a disagreement. Soulmate phase: Last Quarter (see First Quarter and Last Quarter compatibility).

What does a Waxing Gibbous birth phase mean?

A Waxing Gibbous birthday falls 9.2 to 12.9 days after the New Moon, with 69.1 to 96.2% lit. More than half the Moon was lit and the light was still growing. It rose in the afternoon and stayed up for much of the night, setting after midnight.

Lunar astrology links it with refinement, analysis and patience. Waxing Gibbous people are described as careful and detail-minded, and slow to call anything finished. Soulmate phase: Waning Crescent (see Waxing Gibbous and Waning Crescent compatibility).

What does a Full Moon birth phase mean?

A Full Moon birthday falls within about 1.8 days of the exact Full Moon, with 96.2 to 100% lit. The whole face was lit. It rose around sunset and set around sunrise, so it was up all night. Your result can read a few percent short of fully lit, because the label covers the days either side of the peak.

Lunar astrology links the Full Moon with fulfillment, awareness and openness. Full Moon people are described as expressive and intense, with little left unsaid. Soulmate phase: New Moon (see New Moon and Full Moon compatibility).

What does a Waning Gibbous birth phase mean?

A Waning Gibbous birthday falls 16.6 to 20.3 days after the New Moon, with 96.2 to 69.1% lit. More than half the Moon was lit, but the light was shrinking, now on the left in the Northern Hemisphere. It rose after dark and stayed up into the morning, so it was often still visible after sunrise.

Lunar astrology links it with sharing, teaching and gratitude. Waning Gibbous people are described as generous with what they’ve learned. Soulmate phase: Waxing Crescent (see Waning Gibbous and Waxing Crescent compatibility).

What does a Last Quarter birth phase mean?

A Last Quarter birthday falls 20.3 to 24.0 days after the New Moon, with 69.1 to 30.9% lit. Half the Moon was lit again, the left half in the Northern Hemisphere. It rose around midnight and stood high in the sky at sunrise, so you could often see it in the morning.

Lunar astrology links it with reassessing, release and changing your mind. Last Quarter people are described as restless in a useful way, willing to question what they’ve built. Soulmate phase: First Quarter (see First Quarter and Last Quarter compatibility).

What does a Waning Crescent birth phase mean?

A Waning Crescent birthday falls 24.0 to 27.7 days after the New Moon, with 30.9 to 3.8% lit. The Moon was a thin crescent lit on the left in the Northern Hemisphere. It rose shortly before dawn and sat low in the east just before sunrise. A few days later it vanished and the cycle started over.

Lunar astrology links it with rest, surrender and reflection. Waning Crescent people are described as inward and calm, and at their best with room to step back. Soulmate phase: Waxing Gibbous (see Waxing Gibbous and Waning Crescent compatibility).

Does birth time change your birth moon phase?

Only if your birth date includes a phase change, which is true of about one date in four. A phase lasts about 3.7 days on average, so about three birth dates in four sit entirely inside one phase. The other one in four includes a change at some point in the day, and for those the result can depend on the hour and the time zone you were born in.

So does your birth hour matter? For that one date in four, yes. For the rest, it doesn’t.

Can one birth date have two moon phases?

Yes. On 21 March 1991, the Moon crossed from Waxing Crescent into First Quarter at about 13:00 UTC. Someone born that morning and someone born that evening got different phases:

Same date, two phases. You’d think a birthday would point to one Moon, and nobody warns you it might not.

Here’s the deal with the calculator: without a birth time, it checks the whole UTC day and shows the phase at 12:00 UTC. If the Moon crossed a boundary at any point that day, the result says so and names both phases, as it would for 21 March 1991.

How do I get an exact answer with my birth time?

Choose Add birth time, then enter the time and the time zone you were born in. The calculator converts it to UTC first.

1. Select Add birth time.
2. Enter the time from your birth certificate or hospital record.
3. Enter the time zone of the place you were born.
4. Read the result, which now shows the phase at your exact time.

The UTC date can differ from your local one: a birth at 9 pm in Los Angeles in March falls on the next day in UTC. The Moon doesn’t care about time zones. Your birth certificate does. The good news is the calculator handles that conversion for you.

If your paperwork doesn’t list a time, look for the long-form birth certificate, since short “abstract” versions often leave it off. Ask a parent, too. Baby books and hospital paperwork sometimes have it written down. Don’t guess an hour, because a guess can put you on the wrong side of the change.

How does the birthday moon phase calculator work?

It measures the angle between the Sun and the Moon on your birth date, then turns that angle into a percent lit and one of eight phases. Both positions are measured along the ecliptic, the path they trace across the sky. They come from the series in Jean Meeus’s Astronomical Algorithms, cut down to its largest terms, and the whole calculation runs in your browser.

1. Find both positions. With no birth time, the calculator uses 12:00 UTC on your date. With a birth time and time zone, it converts them to UTC first.
2. Measure the angle. It takes the Moon’s position minus the Sun’s, wrapped to 0–360°.
3. Work out how much is lit. The share lit is (1 − cos of the angle) ÷ 2. At 45° that’s about 15%, and at 135° about 85%.
4. Pick the phase. The eight phases are 45° slices centered on 0°, 45°, 90° and so on, which is why each one lasts about 3.7 days.

So why trust a calculator that runs in your browser? We tested it against the PyEphem astronomy library on 3,000 dates between 1900 and 2100. The largest difference in the Moon–Sun angle was 0.036°. Turns out that’s about four minutes of Moon motion, far finer than a calendar date needs.

The full method is on How We Calculate Moon Phases. If you cross-check against an almanac, find out which time zone it uses first, since phase times often appear in UTC.

How do I compare my moon phase with someone else’s?

Enter both birthdays in the moon phase compatibility calculator. It shows each person’s phase, how many steps apart the two phases are, and one of five pairing types:

• Twin Flames
• Neighbors
• Quarter Cycle
• Near Opposites
• Moon Soulmates

Every phase has exactly one soulmate phase, the one on the opposite side of the cycle, so the two lit portions add up to a whole Moon. Each phase entry above names its soulmate.

Bottom line: the pairing describes the distance between two phases in the cycle. It doesn’t predict whether a relationship will work. No exceptions.

Birthday moon phase FAQs

What moon phase was I born under?

It’s the phase the Moon was in on your birth date. Enter your full birth date, year included, in the calculator above. The date alone decides it unless you were born close to a phase change, and then the card names both phases.

How do I find the moon phase on my birthday by hand?

Look up the last New Moon before your birthday, count the days since, and match the number to the table above. A count under 1.8 or over 27.7 days means New Moon. Expect up to half a day of error, since the Moon’s speed varies.

What did the Moon look like on my birthday?

It looked like the phase shown in your result’s dial, anywhere from a dark disc to a full one. In the Northern Hemisphere, the right side was lit while it grew and the left while it shrank. The Southern Hemisphere sees the reverse.

Does my birth time or time zone change my moon phase?

Only if your birth date includes a phase change, which is true of about one date in four. The result flags those dates and names both phases. Choose Add birth time to enter your time and time zone for an exact answer.

Why does another site show a different moon phase for my birthday?

Sites often check a different time of day, use a simpler formula or work in a different time zone. That matters most on dates with a phase change, where two sites can both be right. Add your birth time here to settle it.

Is my birth moon phase the same as my moon sign?

No. Your moon phase is the angle between the Moon and the Sun, which cycles over about 29.5 days. Your moon sign is the zodiac sign the Moon was in, which changes about every 2¼ days. This calculator covers moon phase only.

What does my birth moon phase mean?

In lunar astrology, each of the eight phases stands for a stage of a cycle, such as beginning, building, completing or releasing. People use the idea as a prompt for reflection. No scientific evidence shows that your birth moon phase predicts your personality or relationships.

How accurate is a birthday moon phase calculator?

The phase is accurate to within 0.036° on our 3,000 test dates against an independent astronomy library, about four minutes of Moon motion. The days-since-the-New-Moon figure is an estimate and can be off by up to half a day. The meanings are symbolic, not scientific.

Are more babies born on a Full Moon?

No. Large studies of birth records haven’t found a reliable link between the Moon’s phase and the number of births. Your birth phase is a calendar fact, so it’s no sign of an unusual birth.