Around the world, the midday siesta is not just accepted, it's a part of the culture, built in to the afternoon for as long as anyone can remember. And recent neuroscience backs up this ancient knowledge; that not only can a 20-minute rest relax your body and mind, but it can also refresh you more fully than a cup of coffee for the afternoon ahead.

In fact, not only will you feel better, naps can actually make you smarter, by giving your brain a reset in the middle of the day.

“Sleep not only rights the wrong of prolonged wakefulness but, at a neurocognitive level, it moves you beyond where you were before you took a nap,” said Matthew Walker, an assistant professor of psychology at UC Berkeley in a university bulletin.

It's research like this that has led some companies to promote nap time for hardworking employees. Companies from Apple to the Huffington Post to Google promote the practice.

So we're convinced that naps are good for body and brain. The next question is: How long should we nap for optimum results? Turns out it depends on what we need. 

Short naps, generally, are best. A 15-20 minute rest—oftentimes called a "power nap"—is proven to refresh your mind and increases overall energy and alertness. You don't fall into a deep sleep in this amount of time, and it's pretty easy to wake up after a shorter kip (Aussie slang for a short sleep). 

A half-hour nap can be a few minutes too long. Thirty minutes is about how much time it takes for your body to drop into deeper stages of sleep. Waking up can be harder when you sleep for a half-hour, so you might feel groggy when you wake.

An hour's nap can work well (and has been found to be particularly good for boosting memory). Long naps of 90 minutes can be useful if you don't get enough sleep at night, as that is the length of a complete sleep cycle — so this resting length improves memory and creativity.

Now of course, everybody's body is different, so it may take more—or less—time for your body to fall asleep and dip into deep sleep, meaning grogginess upon waking. A good way to figure out what works for you is to start with a 10-12 minute rest (if that's all you need, that's great), then work your way up.

As an experienced fan of napping, I have found that I almost always end up napping for 21-24 minutes — that's about when I naturally wake up feeling good, usually before my alarm goes off (it's always a good idea to set an unobnoxious alarm—something really rude can jolt you awake, and undo the relaxation you have achieved). I'm awake, relaxed, and ready for the afternoon. Why this length of time? Well, it takes me a solid five minutes to quiet my mind and body and even get to the beginnging stages of a nap, so even though my actual rest is only 15 minutes or so, I have to have that extra five minutes at the top. 

That's what works for me; but what works for you may be different, and it's worth figuring it out, because a solid nap can mean greater focus and a more relaxed afternoon at the same time, which for me is a coveted state. One caveat: If you find yourself passing out completely (when I nap, I'm always about 15% 'awake' or aware) and you're going into a deep sleep every time you try to nap, you aren't getting enough sleep at night, and no midday nap can help major sleep deprivation, so take care of that part of your sleep first. 

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