How much sleep do you need to operate most efficiently during the day? Are you sleeping enough—or too much? Try this exercise and find out:

• Go to bed 15 minutes earlier than your usual bedtime and wake up at your normal time. The next day, gauge your response. Are you less tired? More alert? Do you generally feel better? If so, add another 15 minutes of sleep the next night. Keep going until you find a bedtime that leaves you feeling great the entire day that follows. That’s your optimal bedtime.

• If you’re wondering if you need less sleep, go to bed 15 minutes later than your usual bedtime, and wake up at the same time the next day. If you experience no difference in alertness or level of fatigue, try cutting back by another 15 minutes each night until you discover the right amount of sleep for you.

adapted from What Your Doctor Hasn’t Told You and the Health Store Clerk Doesn’t Know by Edward L. Schneider, M.D. (Avery, 2006).