Look under the tail
Female: anus and vulva are close together
Female: vulva looks like a vertical slit
Female: the area may resemble an exclamation mark
Male: anus and penis opening are farther apart
Male: genital opening looks more like a small round dot
Male: the area may resemble a colon
Male: testicles may be visible as two small bulges
Compare the distance between openings
Check for presence of testicles if the cat is old enough
If unsure, ask a veterinarian