What to do with the number
- Set an alarm for the power-nap time if you need to be sharp right after. 20 minutes keeps you out of deep sleep.
- Use the full-cycle time when you have 90 minutes free and a real sleep deficit.
- Nap before mid-afternoon so it does not push your bedtime later.
Common questions
What is the best nap length?
About 20 minutes for alertness without grogginess, or a full 90-minute cycle. Naps of 30 to 60 minutes often end in deep sleep and leave you groggy.
Why do I feel worse after a nap?
That is sleep inertia: waking from deep sleep. A shorter nap, or a full cycle, avoids it.
One thing this cannot do
It cannot know how tired you are. After a short night you may fall into deep sleep faster, so a 20-minute nap can still feel heavy.
Sources: NIH StatPearls, Physiology, Sleep Stages · CDC, About Sleep.General information, not medical advice.