Most years have 12 full moons, with one full moon occurring approximately every 29.5 days, which corresponds roughly to one per month

. However, because the lunar cycle (about 354 days for 12 full moons) does not perfectly align with the solar calendar year (about 365.25 days), about every 2½ to 3 years there are 13 full moons in a year. This extra full moon is often called a "blue moon"

. For example, in 2025, there will be 12 full moons, as the previous year 2024 had 13 full moons

. In summary:

• Typical year: 12 full moons
• Occasionally (every 2½ to 3 years): 13 full moons (including a blue moon)

This pattern arises because the lunar calendar is shorter than the solar calendar, causing the full moon dates to shift each year relative to our calendar