The animals mate at the end of the dry season, and at the beginning of a rainy season (from August to October).

An excerpt from the article 20 facts about Sloth
Both the search for mates, pairing, an act of copulation and the birth of the offspring take place in the treetops. Usually, a female gives birth to one young per year and feeds it for six months. Since sloths do not build nests, their offspring are attached to the mother’s body until they grow up. Sloths reach sexual maturity after three years.