Middle adulthood (or midlife) refers to the period of the lifespan between young adulthood and old age. This period lasts from 20 to 40 years depending on how these stages, ages, and tasks are culturally defined. The most common age definition is from 40 to 65, but there can be a range of up to 10 years (ages 30-75) on either side of these numbers.

Though the exact range is disputed, most sources place middle adulthood between the ages of 45-65. This phase of life is marked by gradual physical, cognitive, and social changes in the individual as they age. This time span can be referred to as 'middle age' and has been defined as the time between ages 45 and 65.