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Lunar Phase on Date Calculator

Moon phase, age, and illumination for any date.

Compute the Moon's phase, age in days, and illuminated fraction for any date, plus the next new- and full-moon dates. Uses a known new-moon reference and the mean synodic month (29.5306 d).

Dr. Helena Ortiz By Dr. Helena Ortiz
Published Last reviewed 1 min read

Inputs

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

Age = (JD − 2451550.1) mod 29.5306. Illumination = (1 − cos(2π · age / 29.5306)) / 2.

In depth

Compute the Moon's phase, age in days, and illuminated fraction for any date, plus the next new- and full-moon dates. Uses a known new-moon reference and the mean synodic month (29.5306 d).