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Moon Sign Calculator

Find your moon sign and the moon phase at your birth, computed from the lunar position rather than a lookup table.

Written by Jude Ramsey · Last updated August 2026 · How these calculators are checked

Understanding the moon sign calculation

The Moon travels roughly thirteen degrees a day and changes sign every two and a half days, which is why a moon sign cannot be read off a birth date alone — people born on the same date hours apart can have different moon signs.

This calculator uses the main periodic terms of the lunar theory, giving a position accurate to about a fifth of a degree. That is comfortably enough to identify the sign except within a few minutes of a cusp, which the calculator flags.

Worked example

As an example, with a longitude of -0.13, the calculator returns a moon sign of ♑ Capricorn. Underneath, Exact degree comes out at ♑ Capricorn 27° 56′ and Sun sign at ♊ Gemini 23° 59′. Change any field and every figure updates as you type.

How to use it

  1. Enter your birth date and time.
  2. Enter the UTC offset for that place and date.
  3. Read the moon sign, exact degree and phase.

Formula reference

lunar longitude = mean longitude + 6.289·sin(M) + 1.274·sin(2D−M) + 0.658·sin(2D) + smaller terms moon phase from the elongation between the Moon and the Sun

FAQ

Why does the moon sign change so often?
Because the Moon orbits Earth in about 27 days, covering all twelve signs in that time — roughly two and a half days each.
Do I need my exact birth time?
Less than for the ascendant, but it helps. If you were born near a sign change, a few hours can flip the answer.
What is the moon phase at birth?
How far the Moon had travelled from the Sun at that moment, from new through full and back. It is shown alongside the sign.

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