A blood moon, which is a total lunar eclipse where the moon appears reddish, typically happens about every 2 years or so. Usually, there are about two to four lunar eclipses each year, but not all are total eclipses that produce the blood moon effect. On average, total lunar eclipses (blood moons) can be seen roughly every 1.5 to 2 years from any one location, but the exact frequency varies. Lunar tetrads, which are four total lunar eclipses in a row spaced about six months apart, are rarer and happen several times per century but not every year.
For context, in astronomy, the term blood moon specifically refers to the reddish color seen during a total lunar eclipse due to Earth's atmosphere filtering sunlight. The frequency depends on the moon's and Earth's alignment and the observer's location. (Note: Some results referred to "blood moons" in video games like Zelda and Terraria, which have different mechanics unrelated to real astronomy).
