Nearly all people, whether they consider themselves sleep deprived or not, can initially obtain extra sleep. However, as accumulating extra sleep reduces carryover sleep debt, a point is reached where it is no longer possible to obtain extra sleep. If there were a practical method to make a precise measurement of a person's daily sleep requirement, it may be possible to show that most individuals are carrying a very large sleep debt. Several observations and studies demonstrate that almost everyone is sleep deprived and carries some amount of sleep debt. How long such an indebtedness will persist without change if no extra sleep is obtained is not known.