Males and females generally come together only to mate.
Subadult males (unflanged) will try to mate with any female and will be successful around half the time.
Dominant flanged males will call and advertise their position to receptive females, who prefer mating with flanged males.
Adult males will often target females with weaned infants as mating partners because the female is likely to be fertile.

Females reach sexual maturity and experience their first ovulatory cycle between about six and 11 years of age, although females with more body fat may experience this at an earlier age.
The estrous cycle lasts between 22 and 30 days and menopause has been reported in captive orangutans at about age 48.
Females tend to give birth at about 14–15 years of age.
Newborn orangutans nurse every three to four hours, and begin to take soft food from their mothers' lips by four months.
During the first year of its life, the young clings to its mother's abdomen by entwining its fingers in and gripping her fur.
Offspring are weaned at about four years, but this could be much longer, and soon after they start their adolescent stage of exploring, but always within sight of their mother.
During this period, they will also actively seek other young orangutans to play with and travel with.
On average, juveniles do not become completely independent until they are about seven years of age.
The birth rate for orangutans has been decreasing largely due to a lack of sufficient nutrients as a result of habitat loss.

A 2011 study on female orangutans in free-ranging rehabilitation programs found that individuals that were supplemented with food resources had shorter interbirth intervals, as well as a reduced age, at first birth.
Males and females generally come together only to mate. Subadult males (unflanged) will try to mate with any female and will be successful around half the time. Dominant flanged males will call and advertise their position to receptive females, who prefer mating with flanged males. Adult males will often target females with weaned infants as mating partners because the female is likely to be fertile.
Females reach sexual maturity and experience their first ovulatory cycle between about six and 11 years of age, although females with more body fat may experience this at an earlier age. The estrous cycle lasts between 22 and 30 days and menopause has been reported in captive orangutans at about age 48. Females tend to give birth at about 14–15 years of age. Newborn orangutans nurse every three to four hours, and begin to take soft food from their mothers' lips by four months. During the first year of its life, the young clings to its mother's abdomen by entwining its fingers in and gripping her fur. Offspring are weaned at about four years, but this could be much longer, and soon after they start their adolescent stage of exploring, but always within sight of their mother. During this period, they will also actively seek other young orangutans to play with and travel with. On average, juveniles do not become completely independent until they are about seven years of age. The birth rate for orangutans has been decreasing largely due to a lack of sufficient nutrients as a result of habitat loss.
A 2011 study on female orangutans in free-ranging rehabilitation programs found that individuals that were supplemented with food resources had shorter interbirth intervals, as well as a reduced age, at first birth.
Bornean orangutan