How do tell if your red eared slider is a boy or a girl?

Male Red eared sliders have a thicker tail base and long claws used to help in mating also they have a slight indent on their tummies to again help with mating. Females lack these attributes, therefor they have smaller claws tails tend to be thinner at the base of their tail and no concave to belly. Obviously it is easier to tell if you have several to compare :). If there is any doubt be sure to supply an area where the turtle can haul out and lay eggs in subtrate or they may hold the eggs and suffer from egg binding a potentially fatal condition.