Naps

A nap can go wrong in two ways. The first is waking from it slower and foggier than before you lay down. The second shows up hours later, when a nap taken late in the day leaves you wide awake at midnight. Both are avoidable, and both come from the way the body times sleep.

What a nap takes from the night

Sleep is timed by two systems working alongside each other (Borbély et al., 2016). One is sleep pressure, the drive to sleep, which builds the longer you're awake and is cleared by sleeping. The other is the body clock, which sets the hours when sleep comes easily. Our article on sleep pressure covers both in more detail.

A nap clears some of that pressure hours before bed. A short one clears a little; a long one clears more, and a late one leaves fewer waking hours for the pressure to build back up before lights out. Either way you arrive at bedtime with less drive to carry you into sleep, so it can take longer to drop off.

Short naps and the groggy wake-up

Brooks and Lack (2006) tested nap length directly. They cut the night of 24 healthy young adults, good sleepers who didn't usually nap, to about five hours, then gave them an afternoon nap at 3 pm of 5, 10, 20 or 30 minutes of actual sleep, or no nap. Five minutes of sleep did very little. The 10-minute nap was the best of the set: alertness, mood and performance improved straight away, and some of that lasted up to two and a half hours. A 20-minute nap helped too, although the benefit took about half an hour to show. After 30 minutes people were groggier and slower at first, which is sleep inertia (the heavy, muddled feeling of being woken from sleep), and they only improved once it had passed.

The usual explanation is that the longer you sleep, the more time the brain has to settle into deeper sleep, which is harder to surface from. The study itself shows the pattern without settling the reason. It was also done after a short night, in young adults, so we take it as a guide to how long a nap should be rather than a measure of how much it will help you.

Why timing matters as much as length

Mograss and colleagues (2022) gave 62 healthy young adults wrist-worn movement trackers for eight days. Naps taken within seven hours of night sleep went with taking longer to fall asleep and waking more often in the night, and nap length (under or over an hour) made no measurable difference on its own. People who napped three or more times in the eight days had more broken nights than those who napped less. It was observational, so it shows a link rather than proof, and other researchers have questioned parts of it.

A small trial points the same way from the other side. Boukhris and colleagues (2026) gave 14 student athletes either no nap, a 25-minute chance to nap or a 90-minute chance, each ending at 15:00, and tracked their sleep that night with a wrist device. Neither nap disturbed the night. Taken together, they fit the idea that the gap between a nap and bedtime matters more than the nap's length, though both studies were small and in young adults.

How your plan uses this

We count back from your own usual lights out rather than using one clock time for everyone. Keep a nap to about 20 minutes and finish it at least 8 hours before you usually turn the light out: for someone who sleeps at 23:00 that means done by 15:00, and earlier for an earlier sleeper. The 7-hour line in the Mograss study is the only boundary the research gives; we've added an hour's margin. These are working rules built from the findings above, and no trial has tested them exactly. If falling asleep at night is your main difficulty, your plan may ask you to skip naps altogether for the fortnight, so all of the day's sleep pressure is there at bedtime.

Your diary records naps and dozes, which lets us see whether changing them changes your nights.

If you need to nap most days despite a full night in bed, or you nod off without meaning to, mention it to your GP, because it can be a sign of a sleep condition that needs looking at. Our article on daytime sleepiness explains what that means for driving.