Gently lift the kitten’s tail
Look at the shape and spacing of the openings
Female kittens usually have a vertical slit close to the anus
Male kittens usually have a round opening farther from the anus
Female: anus and vulva look like an upside-down exclamation mark
Male: anus and penis opening look more like two dots with more space between them
Check for any developing testicles in older kittens
Compare with a known male and female kitten if possible
Ask a veterinarian if you are unsure