Biphasic sleep means sleeping in two blocks in 24 hours instead of one. The most common version is a shorter night plus an afternoon nap, like a siesta. It is popular online as a way to get more done, but the research gives a more careful picture. Here is what biphasic sleep is, what studies show, and how to try it safely if it suits your life.
In this article
The short answer
- Biphasic sleep usually means a main night of sleep plus one daytime nap.
- A short nap (10 to 20 minutes) after a normal night is safe and can boost alertness.
- Splitting sleep does not reduce how much sleep you need. Adults still need 7 hours or more in total.
- In one study, split sleep helped alertness but raised blood sugar more than continuous sleep.
- Regular naps of an hour or more are linked with worse health in large studies.
What biphasic sleep is
Most adults today are monophasic: they sleep once, at night. Biphasic sleep adds a second sleep period. There are two main versions:
- Siesta style: about 6 to 7 hours at night, plus a nap of 20 to 90 minutes in the early afternoon.
- Segmented style: two blocks at night with an hour or so awake in between. This is the “first sleep” and “second sleep” that historians describe. We cover it in segmented sleep vs biphasic napping, and what waking in the night may do to melatonin and other hormones in segmented sleep and your hormones.
Polyphasic schedules, with three or more short sleeps a day, are a different thing. They cut total sleep a lot and are not recommended.
Why the afternoon nap feels natural
Many people feel a dip in alertness in the early afternoon, often between 1 and 3 PM. This “post-lunch dip” happens even if you skip lunch. It comes from your body clock and from the sleep pressure that builds up from the moment you wake. A nap during this dip is easy to fall into, which is one reason siesta cultures exist in many warm countries.
Not everyone naps naturally, though. A 2015 study of three hunter-gatherer groups without electricity found that they mostly slept in one block at night.
What the research shows
Short naps help alertness
In a 2006 study, adults who had slept only 5 hours took naps of different lengths at 3 PM. A 10-minute nap gave the best overall result: they felt more alert straight away, and some benefits lasted over 2 hours. A 30-minute nap first caused grogginess, called sleep inertia, before the benefits started. Read more in our guide to nap timing and sleep inertia.
Split sleep is not a free lunch
A 2019 study in Singapore compared teenagers who slept either 6.5 hours in one block, or 5 hours at night plus a 1.5-hour afternoon nap. The split-sleep group was more alert and had better memory and mood. But their blood sugar rose more in a glucose test. Both groups did worse than teens who slept 9 hours at night. The researchers’ advice was simple: get enough sleep at night.
The siesta and heart health
A Greek study of more than 23,000 adults found that people who took a regular siesta had a lower rate of death from heart disease over about 6 years. This kind of study shows a link, not cause and effect. People who can nap may also have less stressful lives.
Other large studies point the other way for long naps. A 2015 analysis of 11 studies with over 150,000 people found that naps of 60 minutes or more a day were linked with a higher risk of heart disease and death. Naps under an hour showed no extra risk. Long naps may be a sign of poor night sleep or illness, rather than the cause.
Myth vs fact
Myth: Biphasic sleep lets you get by on less sleep. Fact: It changes when you sleep, not how much you need. If the night block gets shorter, the nap has to make up the difference.
Who biphasic sleep may suit
- People whose work or culture already allows a midday break.
- Shift workers who need a planned nap before a night shift. See our night shift guide.
- Older adults who sleep less at night and naturally nap, as long as night sleep is not getting worse.
Who should be careful
- People with insomnia. Naps reduce sleep pressure, which can make it harder to fall asleep at night. Insomnia treatment usually asks you to stop napping.
- People who are very sleepy in the day even after a full night. That needs checking by a doctor first.
- Teenagers. They need 8 to 10 hours, and the study above suggests night sleep is better for their blood sugar.
How to try a biphasic schedule
Try this
- Keep your night sleep first. Aim for at least 6 hours at night, and 7 or more hours in total.
- Nap early. Between about 1 and 3 PM. Late naps make it harder to sleep at night.
- Choose a length. 10 to 20 minutes for a quick lift. About 90 minutes for a full sleep cycle if the nap is part of your main sleep plan.
- Avoid 30 to 60 minutes if you need to be sharp right after, because you may wake from deep sleep feeling groggy.
- Keep it regular. Same nap time and same wake-up time every day.
- Track it for two weeks. If you sleep worse at night, or feel worse in the day, go back to one block.
When to see a doctor
Needing a long nap every day, or falling asleep without meaning to, is not normal tiredness. It can be a sign of sleep apnea, narcolepsy, depression or a medical problem. See a doctor if you feel very sleepy in the day despite a full night in bed, or if you snore loudly.
Frequently Asked Questions
Is biphasic sleep healthier than sleeping once?
There is no good evidence that it is healthier. A short nap on top of a full night is fine for most people. Cutting night sleep to make room for a nap may raise blood sugar and leaves you short on sleep overall.
How long should the nap be on a biphasic schedule?
For a quick lift, 10 to 20 minutes. If the nap is meant to replace part of your night, about 90 minutes lets you finish a full sleep cycle. Keep naps under an hour a day unless a doctor advises otherwise.
How long does it take to adjust?
Most people need one to two weeks of keeping the same times every day. If you still feel worse after that, the schedule may not suit you.
Can biphasic sleep help with ADHD or shift work?
A planned nap before a night shift can improve alertness at work. For ADHD there is no good research on biphasic schedules, so talk to your doctor before changing your sleep.
Conclusion
Biphasic sleep is not a hack for needing less sleep. It is a different way to spread the sleep you need. A short early-afternoon nap after a full night is safe and can help. If you want to move part of your night into the afternoon, keep your total at 7 hours or more, keep the nap early, and watch how you feel.
Sources
- Watson NF, et al. Recommended amount of sleep for a healthy adult: a joint consensus statement of the AASM and Sleep Research Society. Sleep, 2015.
- Brooks A, Lack L. A brief afternoon nap following nocturnal sleep restriction: which nap duration is most recuperative? Sleep, 2006.
- Lo JC, et al. Differential effects of split and continuous sleep on neurobehavioral function and glucose tolerance in sleep-restricted adolescents. Sleep, 2019.
- Naska A, et al. Siesta in healthy adults and coronary mortality in the general population. Arch Intern Med, 2007.
- Yamada T, et al. Daytime napping and the risk of cardiovascular disease and all-cause mortality: a dose-response meta-analysis. Sleep, 2015.
- Yetish G, et al. Natural sleep and its seasonal variations in three pre-industrial societies. Curr Biol, 2015.
- Edinger JD, et al. Behavioral and psychological treatments for chronic insomnia disorder in adults: an AASM clinical practice guideline. J Clin Sleep Med, 2021.
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