How to Find Your Natal Moon Phase From Your Birth Chart

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Finding your natal Moon phase takes two numbers from your chart and one subtraction. This page walks through the method with three calculated example charts, then covers the cases that need extra care: results close to a boundary and charts without a birth time. What the phases are, and why the direction of the measurement matters, is explained in natal Moon phases explained.

Calculator note: The Astrologist.com birth chart does not calculate or label Moon phases. It shows the Sun and Moon by sign, degree and minute, and the phase described here is worked out by hand from those two positions. Without a birth time, the chart places the Moon at local noon as a date reference only, so a phase read from that position is not established until the whole birth date has been checked.

What you need

Generate your chart on the free birth chart with your birth date, time and place. In the planet table under the wheel, note two entries: the Sun and the Moon, each written as degree, minute and sign glyph, for example 17°52' ♊ for 17 degrees 52 minutes of Gemini. The houses, the Ascendant and the aspect lines play no part in this calculation.

If you do not know your birth time, read the steps anyway, then use the full-day check on Moon phase without a birth time instead of the single chart.

Step 1: turn each position into a longitude

A position like 17°52' Gemini is measured from the start of Gemini. To compare two positions in different signs, convert each to its distance from 0° Aries, the ecliptic longitude. Add the sign's starting value to the degrees, and divide the minutes by 60:

So 17°52' Gemini is 60 + 17 + 52/60 = 77.87°.

Step 2: subtract the Sun from the Moon

Take the Moon's longitude minus the Sun's. If the answer is negative, add 360. The result, between 0° and just under 360°, is the directed elongation: how far the Moon is ahead of the Sun, counted forward through the signs. Always subtract in this order. Reversing it, or taking the shorter distance between the two, mixes up the waxing and waning halves of the cycle.

Step 3: look up the phase

A value exactly on a boundary belongs to the phase that starts there.

Three worked examples

The positions below come from charts calculated with the free chart's routines, written as the planet table displays them. The people are fictional.

Amsterdam, 9 June 1987, 07:45. Sun 17°52' Gemini = 77.87°. Moon 11°57' Scorpio = 210 + 11.95 = 221.95°. Moon minus Sun = 144.08°. That falls between 135° and 180°: Gibbous, the last waxing phase before the Full Moon.

Leeds, 23 November 1983, 14:10. Sun 0°42' Sagittarius = 240.70°. Moon 9°55' Cancer = 99.92°. Moon minus Sun = minus 140.78°, so add 360: 219.22°. That is the Full phase, already past the exact Full Moon. Had you measured the shorter distance between the two, 140.8°, you would have placed this chart in the waxing Gibbous phase by mistake.

Bristol, 20 July 1990, 09:00. Sun 27°21' Cancer = 117.35°. Moon 3°12' Cancer = 93.20°. Moon minus Sun = minus 24.15°, plus 360 = 335.85°: Balsamic. Both bodies are in Cancer, yet this is not a New Moon birth. The Moon is behind the Sun and a little under two days from catching it. In the London noon charts of 1900 to 2099, half of the dates with the Sun and Moon in the same sign (50.2%) were Balsamic rather than New, and two thirds of New phase dates (66.8%) had the Moon in a different sign from the Sun.

A quick sanity check

Count the signs forward from the Sun's sign to the Moon's, in zodiac order. Each sign is roughly 30°, so the count times 30 should land within 30° of your result. In the Leeds example, Sagittarius to Cancer is seven signs forward, about 210°, which agrees with 219.22°. If the check disagrees badly, the subtraction was probably done in the wrong order.

Results close to a boundary

The planet table rounds each longitude to a hundredth of a degree and shows whole minutes, so an elongation worked out from it can be off by up to about a minute and a half of arc. The Moon gains on the Sun by roughly half a degree an hour, so that is about three minutes of clock time. If your result is within a few minutes of arc of a boundary, the rounding can decide the phase. In that case, settle it with a source finer than the table. For the four principal boundaries, 0°, 90°, 180° and 270°, look up the exact time of the New Moon, First Quarter, Full Moon or Last Quarter in an ephemeris or a published lunar phase table that gives times to the minute, convert it to your birth time zone, and compare it with your birth time. Those tables do not list the intermediate boundaries at 45°, 135°, 225° and 315°. For those, you need Sun and Moon longitudes for your birth time that are more precise than whole minutes of arc, or an ephemeris calculation of the moment the elongation crossed that value. Do not estimate an intermediate crossing from the nearest New, quarter or Full Moon, or by assuming each phase lasts the same number of days; the Moon's speed varies too much for that. If the precision of your time and positions cannot settle it, treat both neighbouring phases as possible. Boundary cases also come up whenever the birth time is uncertain by more than a few minutes; how accurate a birth time needs to be covers testing a time window.

Without a birth time

With no time, the free chart shows the Moon at local noon, marks it with ≈ and draws no Moon aspect lines. That noon position is a reference for the date, not your natal Moon. The phase can change during the day, so run the chart at 00:00 and at 23:59 on your birth date and work out the elongation for both. Moon phase without a birth time explains why those two values bracket every possible phase on that date and what to do when they differ.

After you have your phase

The first four phases are read on born under a waxing Moon and the last four on born under a waning Moon. If your Sun and Moon also form a major aspect, Moon phase vs Sun-Moon aspects explains how the two descriptions relate. To talk through the result alongside the rest of your chart, you can ask the Astrologist.

Related articles

• Natal Moon Phases Explained
• Moon Phase Without a Birth Time
• Birth Chart Calculator Guide
• How to Read a Birth Chart