how often do supermoons happen

Supermoons typically occur about three to four times a year. A supermoon happens when a full Moon coincides with the Moon's closest approach to Earth in its elliptical orbit, called perigee. Because the Moon's orbit changes orientation while Earth orbits the Sun, supermoons do not happen every month but happen several times a year, often consecutively over a few months. The term isn't an official astronomical definition but commonly refers to full moons that are within about 90% of the Moon's closest approach distance to Earth.