Full moons occur about once every 29.5 days, which works out to roughly 12–13 full moons per year.

Basic timing

  • The Moon goes from one full phase to the next in about 29.53 days; this period is called a synodic month.
  • Because this is a bit shorter than a calendar month, some years have 13 full moons instead of 12.

Why it’s not exact

  • The Moon’s orbit is slightly elliptical and tilted, so the exact interval between full moons can vary by several hours around the 29.5‑day average.
  • Time zones also mean a full moon might fall on different calendar dates in different parts of the world, even though it is the same instant in time.

Yearly pattern

  • In a typical year you see one full moon per month, with an occasional year having two full moons in one month, giving 13 in that year.
  • When two full moons occur in a single calendar month, the second one is popularly known as a “blue moon.”

TL;DR: You get a full moon about every 29.5 days, so expect 12–13 full moons each year.