Biphasic sleep

People in Europe before electric light often slept in two parts, according to the historian Roger Ekirch (Ekirch, 2016). He has written that a “first sleep” and a “second sleep” were common there all year round. People woke around midnight or later, and thought nothing of it.

Not every researcher agrees that all people slept this way. One team measured the sleep of 3 groups who live without electricity, in Africa and South America (Yetish and colleagues, 2015). Those groups slept in one stretch at night, and did not nap on most days.

Ekirch answered that he did not claim people everywhere slept in two parts. So the question is still open. Either way, this is history. It does not show what is right for a person now.

Biphasic sleep has not been studied much, and most of the studies are about a night plus a nap. Here is what three sources say.

The total is what counts.

A panel of US sleep experts read the lab studies in which people slept too little (Watson and colleagues, 2015). The panel wrote that the total sleep in 24 hours is what matters for how people do on tests of attention and thinking. Schedules that split sleep followed the same pattern as one block: less sleep in all, worse results.

A night plus a nap helped afternoon memory in one study.

In one study, teenagers lived at a boarding school for two weeks (Cousins and colleagues, 2021). Some slept only at night. Others had a shorter night and a 90-minute nap in the afternoon, with the same total time set aside for sleep. The nap groups remembered more of what they learned in the afternoon. For what they learned in the morning, there was no difference.

The nap groups also slept a little less in all, and the researchers could not rule out other downsides. The study lasted two weeks and was done with teenagers. It does not show what sleeping in two parts does to an adult over months.

A US health agency says to keep naps short.

The NHLBI, a US health agency, says a nap in the day may make you more alert, and that adults should nap for no more than 20 minutes. It also says people who have trouble falling asleep at night should limit naps, or take them earlier in the afternoon.

Polyphasic sleep is sleeping in several short blocks spread across the day and night. Some people who promote these schedules say they do well on as little as 2 hours of sleep a day.

A panel of sleep researchers, brought together by the National Sleep Foundation, went through the published studies (Weaver and colleagues, 2021). Its report says three things:

• The panel found no evidence that polyphasic schedules have benefits.
• Polyphasic schedules, and the lack of sleep that comes with them, are linked to worse health of body and mind and to worse performance.
• The panel does not recommend trying to follow a schedule that cuts the sleep in 24 hours by a lot, or one that breaks sleep into many pieces across the day.

The panel left nap and siesta schedules out of its review, so its findings are about many short sleeps and not about a night plus one nap.

Sleep that comes in pieces is not always a choice. The CDC, the US public health agency, says to talk to a healthcare provider if you often have problems sleeping. The signs it lists include waking again and again in the night, and feeling tired even after enough sleep. The NHLBI says to talk to your doctor if you think you sleep too much or too little.

This page reports what studies and sleep organizations say. It is not medical advice, and it does not say that any schedule is safe or good for you.

You know how much you sleep in two blocks by writing both down and adding them. A nap is easy to forget, and a night with a gap in the middle is easy to count as one long night. The sleep debt calculator adds up a week.

A good way to keep this count takes the hours from what you already write or say about your day, with no timer to start. Most journaling apps only ask how you slept. They do not add up the hours.

One app built for this is Think in Numbers, a smart journaling app with time tracking built in.

You write or say your day in your own words, as it happens or all at once. The app reads what you wrote and counts the hours that went to each part of it: sleep, naps, your phone in bed, and the time you never mentioned (shown as unaccounted). Then it shows those hours over days and weeks. So you can see the hours of each block of sleep you wrote down, day by day. Add the afternoon nap as a daily habit. On each day you write that you took it, the app ticks it off.

1. You write your day

2. It counts the hours

• Nap0m
• Work0m
• Sleep0m
• Unaccounted24h

3. It shows your week

S

M

T

W

T

F

S

Nap this week: 0m

On 6 of 7 days. The gap is the day without it.

An example day and week.

Play again

Write my first day

Download on the App StoreGet it on Google Play

Or scan with your phone's camera.

For iPhone and Android. Try it on your own day before you pay.

Every finding on this page links to one of the sources below. We checked each one again on October 13, 2026. For the panel’s report on polyphasic sleep we could open the summary but not the whole report.

1. Watson and colleagues (2015). Recommended amount of sleep for a healthy adult: a joint consensus statement of the American Academy of Sleep Medicine and Sleep Research Society. J Clin Sleep Med.
2. Ekirch, A. R. (2016). Segmented sleep in preindustrial societies. Sleep, 39(3), 715 to 716.
3. Yetish, G., Kaplan, H., Gurven, M., Wood, B., Pontzer, H., Manger, P. R., Wilson, C., McGregor, R. and Siegel, J. M. (2015). Natural sleep and its seasonal variations in three pre-industrial societies. Current Biology, 25(21), 2862 to 2868.
4. Consensus Conference Panel: Watson, N. F., Badr, M. S., Belenky, G., Bliwise, D. L., Buxton, O. M., Buysse, D. and others (2015). Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society on the Recommended Amount of Sleep for a Healthy Adult: Methodology and Discussion. Sleep, 38(8), 1161 to 1183.
5. Cousins, J. N., Leong, R. L. F., Jamaluddin, S. A., Ng, A. S. C., Ong, J. L. and Chee, M. W. L. (2021). Splitting sleep between the night and a daytime nap reduces homeostatic sleep pressure and enhances long-term memory. Scientific Reports, 11, 5275.
6. National Heart, Lung, and Blood Institute (read October 1, 2026). Healthy Sleep Habits.
7. Weaver, M. D., Sletten, T. L., Foster, R. G., Gozal, D., Klerman, E. B., Rajaratnam, S. M. W., Roenneberg, T., Takahashi, J. S., Turek, F. W., Vitiello, M. V., Young, M. W. and Czeisler, C. A. (2021). Adverse impact of polyphasic sleep patterns in humans: Report of the National Sleep Foundation sleep timing and variability consensus panel. Sleep Health, 7(3), 293 to 302.
8. Centers for Disease Control and Prevention (read October 1, 2026). About Sleep.
9. National Heart, Lung, and Blood Institute (read October 1, 2026). How Much Sleep Is Enough?