A 90-minute nap isn't too long for most adults, as long as you take it in the early afternoon. Ninety minutes is about one full sleep cycle, so you tend to wake from light sleep instead of deep sleep and feel refreshed rather than groggy. The catch is timing: a long nap late in the day can make it hard to fall asleep at night.
Free toolNap CalculatorWhen to set your alarm for a power nap or a full-cycle nap.Why 90 minutes works better than 45 or 60
Sleep runs in cycles of about 90 minutes: light sleep, then deep sleep, then REM, then back to light sleep. How you feel when you wake depends a lot on where in that cycle the alarm lands.
| Nap length | What you wake from | How you're likely to feel |
|---|---|---|
| 10 to 20 min | Light sleep | Alert quickly |
| 30 min | Starting deep sleep | Groggy for a while, then better |
| 45 to 60 min | Deep sleep | Often worse than before the nap |
| About 90 min | Light sleep, end of a cycle | Refreshed, after a few minutes |
| 2+ hours | Partway into a second cycle | Groggy, and night sleep may suffer |
The grogginess from waking out of deep sleep is called sleep inertia. In an Australian study, even a 30-minute nap caused a period of reduced alertness right after waking before the benefits showed up. A 90-minute nap sidesteps most of that by letting you finish the cycle.
What you get from a full-cycle nap
A short nap mostly gives you light sleep. A 90-minute nap also gives you deep sleep and REM, which is why it can do more than a power nap.
In a Harvard study, people who took a 60 to 90 minute nap containing both deep sleep and REM improved on a visual learning task about as much as earlier studies had seen after a full night's sleep. That's one task in one lab, so it doesn't mean a nap replaces a night. But it shows a full-cycle nap can do real work beyond just perking you up.
A 90-minute nap is a good choice when:
- You got a short night and have a long day or evening ahead.
- You're about to start a night shift or a late drive.
- You're learning something and want to help it stick.
- You have a free afternoon and wake easily from naps.
When a 90-minute nap is too long
- It's late in the day. A long nap at 5 PM uses up the sleep pressure you need for bedtime. Keep full-cycle naps to the early afternoon. See the best time to take a nap.
- You have trouble sleeping at night. If you have insomnia, long daytime naps usually make it worse. Stick to 20 minutes or skip naps for a while.
- You need one every day. A daily long nap is often a sign that your nights are too short. Check your sleep debt and use the sleep calculator to fix your bedtime first.
- You only have 60 minutes. Better to take a 20-minute nap than cut a 90-minute nap short in deep sleep.
How to time a 90-minute nap
Set your alarm for 90 minutes plus the time it takes you to fall asleep. If you usually drift off in about 15 minutes, that's 1 hour 45 minutes after you lie down.
| Lie down at | Alarm for a 90-min nap | Alarm for a 20-min nap |
|---|---|---|
| 12:00 PM | 1:45 PM | 12:35 PM |
| 1:00 PM | 2:45 PM | 1:35 PM |
| 2:00 PM | 3:45 PM | 2:35 PM |
| 3:00 PM | 4:45 PM | 3:35 PM |
If you fall asleep faster or slower than 15 minutes, the nap calculator lets you adjust.
Tips for waking up well
- Get up when the alarm goes off. Snoozing can drop you back into a new cycle.
- Get light and move. Open the curtains or step outside for a few minutes.
- Give it 5 to 10 minutes. Even a well-timed nap can leave you a little foggy at first.
- Have a coffee after, not before, if you want a boost and it's early enough in the day. A coffee before a 90-minute nap would kick in while you're still asleep. Check the timing with the caffeine calculator.
If you often nap for 2 hours or more without meaning to, or you nap a lot and still feel exhausted, talk to a doctor. Heavy daytime sleepiness can be a sign of a sleep disorder.