Moon Phase Soulmate

How to find your moon phase

By the Moon Phase Soulmate editorial team · Published

The quickest route is a calculator and the slowest is arithmetic on paper. This guide covers how to find your moon phase by four different methods, and the only thing any of them needs is your birth date, no birth time, no birthplace.

Method 1: use a calculator (fastest)

  1. Open the birthday moon phase calculator.
  2. Enter your birth date. No time, no birthplace.
  3. Read off the named phase and the illumination percentage. The phase links through to its own page.

If you want two people at once, the two-date version returns both phases and the pairing they form. Both run in the browser, so nothing is transmitted.

Method 2: read it from an ephemeris or almanac

  1. Find a table of new and full moon dates for your birth year. Printed astronomical almanacs list these, as do most published ephemerides.
  2. Locate the new moon immediately before your birth date.
  3. Count the days from that new moon to your birth date. This is the Moon's age.
  4. Convert the age to a phase: 0 to 1 days is New Moon, 1 to 7 Waxing Crescent, around 7 First Quarter, 8 to 14 Waxing Gibbous, around 15 Full Moon, 16 to 21 Waning Gibbous, around 22 Last Quarter, 23 to 29 Waning Crescent.

Method 3: the arithmetic, on paper

Use this when you have no internet and no almanac, and accept a little imprecision.

  1. Take a known new moon as a reference. 6 January 2000 is a convenient one: a new moon occurred at 18:14 UT.
  2. Count the whole days between that date and your birth date.
  3. Divide by 29.53, the average length of a lunation.
  4. Take the fractional part of the answer and multiply it back by 29.53. That is the Moon's age in days on your birth date; convert it with the list in Method 2.

The catch, and it is a real one. Individual lunations run from about 29.27 to 29.83 days, so a fixed 29.53-day step accumulates error the further your date sits from the reference. A few decades is enough to name the neighbouring phase. Pick a reference new moon within a year or two of your birth date and this method holds up well; use one from forty years away and it will sometimes be wrong.

Method 4: find a photograph (least reliable)

For a recent date, an image search combining the date with the word moon will often surface a photograph. Treat it as a sanity check rather than an answer: photographs rarely record the hour, and the lit limb appears on the opposite side when the picture was taken from the southern hemisphere, which flips the apparent phase for anyone reading it casually.

When the answer is genuinely ambiguous

Two dates in every lunation fall near a boundary between named phases, and on those dates the phase changes during the day itself. If yours is one of them, you need a birth time and a time zone to settle it, and different calculators will legitimately disagree. Everything else about the mechanics is covered in the lunar cycle explained, and the exact algorithm this site uses is on the the exact algorithm this site runs.