Sea otters breed throughout the year, but their partnerships are temporary. Males may breed with more than one female during the year. 

 Mating generally lasts about 15 to 30 minutes. 

Mating tends to be extremely rough, with males commonly grabbing the females nose with their teeth and dragging them underwater for long periods of time. 

Because of the population bottlenecks that happened in the 18th and 19th century, sea otters today have very low genetic diversity. Inbreeding has become a serious issue. 

The female sea otter's gestation period is typically about 4-6 months. 

Females can delay implantation, which is thought to allow them to put on fat between the weaning of their last pup and birth of the next. 

They usually only give birth to one pup at a time but can occasionally have twins. 

In the northern population births usually occur in the spring and the southern populations give birth in the winter.

Pups are about 3–5 pounds at birth and are born with their eyes open and a full set of teeth. 

Newborn pups are extremely reliant on their mother and are not left alone unless the mother is diving for food. The pups usually lay on their mother's chest while they swim. 

Pups stay with their mother until they are about 4-6 months old and have learned to swim and hunt for their food.

Mothers devote a lot of time to raising their pup, but males provide no parental care. 

Female sea otters reach sexual maturity at 2–5 years of age. Males become sexually mature at 4–6 years of age, but usually don't become active breeders for a few more years. 

Females usually reproduce until they are 10-15 years old.

 The average lifespan in the wild is 10 to 15 years for males and 15–20 years for females. Although some in the wild can live up to 23 years and even longer in captivity.