Lift the tail gently
Look at the shape and spacing of the openings
Male kittens usually have two openings farther apart
Female kittens usually have two openings closer together
Male kittens often show a round anus and a round genital opening
Female kittens often show a round anus and a vertical slit below it
Male kittens may have a slight bulge between the openings
Female kittens usually have a flatter area between the openings
Check for visible testicles only if the kitten is older
Compare with a clear reference image if needed
Ask a veterinarian if you are unsure