Fin whales may be monogamous, as they are often seen in pairs.
Mating occurs in warm, low latitude seas during the winter, and calving usually occurs 12 months later when the populations return again to low latitude. As many as 6 fetuses have been reported, but single births are the norm.
Females probably reach sexual maturity between 3 and 12 years old and will reproduce every 2 or 3 years thereafter. Full physical maturity is not attained until between 25 and 30 years.
Newborns are about 6.5 m in length and weigh 1800 kg. The young are weaned at 6 or 7 months when they are 11 or 12 m in length. Weaned calves travel with their mothers to the winter feeding grounds.