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Free calculator · Astrology

Birth Moon Phase Calculator

The moon phase at your birth follows from the angle between the Moon and the Sun: 0° is new moon, 90° first quarter, 180° full moon, 270° last quarter. The calculator works it out for your birth moment as the UmbraLux app does and names the phase, how much of the Moon was lit, its age since the last new moon and the lunation of your birth.

Date of birth

As exact as you can, ideally from your birth certificate.

Your place is missing? Take the nearest town; a few kilometres hardly change the result.

The calculation runs in your browser. Your birth data is neither sent nor stored; only this device remembers your last entry. · Place data: GeoNames (CC BY 4.0)

How the birth moon phase is calculated

Three steps, from the ephemeris of the UmbraLux app:

  1. 1

    The angle to the Sun

    The Moon's longitude minus the Sun's at your birth moment: the elongation.

  2. 2

    The phase

    New moon, first quarter, full moon and last quarter hold while the Moon is less than 11.25° from the exact angle, 1.6 to 2.1 days. Between them lie the crescent and the gibbous Moon, waxing up to full moon, waning after it.

  3. 3

    Light and age

    Then the lit part of the disc and the time since the last new moon. The exact new moons, full moons and quarters lie within a minute of the US Naval Observatory's tables (checked for 1910, 1950, 1990 and 2025).

Example: 15 May 1990, 14:30, Berlin

The angle between the Moon and the Sun was 243.0°: a waning gibbous Moon, 73% lit, 20.3 days after the new moon of 25 April.

Full moon was on 9 May at 21:31, the last quarter followed on 17 May at 21:46, the next new moon on 24 May at 13:48 (Berlin time).

What the birth moon phase means in astrology

Astrology reads the moon phase at birth as the relation of Sun and Moon, of conscious will and feeling: at new moon they stand together, at full moon opposite each other. A birth under the waxing Moon counts as turned outwards, under the waning Moon as turned inwards.

The calculation is astronomical; what it means is the reading of astrology.

In the library

Questions about the birth moon phase

Do I need my birth time?

Often not: every phase lasts at least a day and a half, and on almost three days in four one phase holds all day. Without a time the calculator names the phase of the day, or the time it changed.

Is the moon phase the same all over the Earth?

Yes, at the same moment everywhere. The birthplace only sets what time that was; from the southern hemisphere the lit side appears mirrored.

What is the Moon's age?

The time since the last new moon. A lunation lasts 29.53 days on average; from 1900 to 2026 between 29.27 and 29.83 days.

How often does a birth fall on a full moon?

The full moon phase covers about 6 percent of the time, the new moon phase as much; the crescents and the gibbous phases just under 19 percent each.

Are more children born at full moon?

Birth records do not show it: an analysis of 564,039 births in North Carolina from 1997 to 2001 found no cluster in any of the eight moon phases over 62 lunar cycles (Arliss and others, 2005).

Is my data stored?

No. The calculation runs in your browser; your date, time and place are neither sent nor stored. Only your device remembers your last entry, and you can delete it below the form.

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