Nap calculator
Last reviewed: 14 September 2026
There are two good nap lengths and one bad one. The bad one is the length most people accidentally choose.
Nap calculator
Tell it when you are lying down and it gives you the alarm times that avoid waking out of deep sleep.
How long should a nap be?
There are really only two good answers, and they sit either side of a gap you want to avoid.
| Length | What happens | Verdict |
|---|---|---|
| 10–20 minutes | You stay in light N1 and N2 sleep and never reach deep sleep. | Best for alertness. You wake clear-headed, and it does not interfere with that night's sleep. |
| 30–60 minutes | Long enough to drop into deep slow-wave sleep, not long enough to come back out of it. | Avoid. This is the nap that leaves you feeling worse than before you lay down. |
| 90 minutes | One complete cycle, including REM, finishing in light sleep. | Best for recovery. Good after a bad night, and you wake at a natural boundary. |
The grogginess after a 45-minute nap is sleep inertia — the same thing that makes a 3:00 AM alarm so brutal. It happens because you were pulled out of deep sleep, and it can take 20 to 30 minutes to clear. It is not a sign that napping does not suit you; it is a sign that the nap was the wrong length.
When to nap
Early afternoon, ideally between 1:00 PM and 3:00 PM. That window coincides with a genuine dip in circadian alertness that almost everyone feels, so you will fall asleep more easily and it costs the least from that night's sleep.
Napping after about 4:00 PM starts to eat into the sleep pressure you have built up during the day, which makes falling asleep at your normal bedtime harder — and that is how one bad night turns into a pattern. If you are genuinely exhausted late in the day, a ten-minute nap costs much less than an hour-long one.
The coffee nap
Drinking a coffee immediately before a 20-minute nap is a real technique with reasonable evidence behind it. Caffeine takes roughly 20 minutes to take effect, and it works by blocking adenosine receptors — while a short nap clears some of the adenosine itself. The two arrive together, and several studies have found the combination beats either alone for alertness and driving performance.
It only works with a short nap, and only if you can fall asleep with a coffee inside you, which not everyone can.
If you cannot fall asleep
Lying still with your eyes closed for twenty minutes is not wasted. Quiet rest measurably reduces subjective fatigue even without sleep, and the pressure to actually fall asleep is usually what stops it happening. Set the alarm, close your eyes, and let it be a rest if it is not going to be a nap.
One caveat worth knowing: if you routinely fall asleep within a couple of minutes of lying down, at any time of day, that is a sign of significant sleep deprivation rather than a talent. Excessive daytime sleepiness despite adequate sleep at night is worth taking to a GP or doctor.
Sources. Age-based recommendations are from the National Sleep Foundation’s sleep duration recommendations and the American Academy of Sleep Medicine’s consensus statements on sleep for healthy children and for adults. Sleep stage figures are from published polysomnography data. This page is general wellbeing information, not medical advice — speak to a GP or doctor about persistent sleep problems.
Common questions
How long should a nap be?
Either 10 to 20 minutes, which keeps you in light sleep and leaves you alert, or 90 minutes, which completes a full cycle. Avoid 30 to 60 minutes — that is long enough to enter deep sleep and not long enough to come out of it, which is what causes the grogginess.
Is a 20 minute nap enough?
Yes, for alertness it is the best-evidenced option. Twenty minutes restores a substantial amount of alertness without entering deep sleep, so there is no grogginess and very little effect on that night's sleep.
What is the best time to nap?
Between about 1:00 PM and 3:00 PM, which lines up with a natural dip in circadian alertness. Napping after 4:00 PM starts to interfere with falling asleep at your normal bedtime.
Why do I feel worse after a nap?
Almost always because the nap was 30 to 60 minutes long and you woke out of deep sleep. That is sleep inertia, and it clears in 20 to 30 minutes. Either shorten the nap to 20 minutes or extend it to a full 90-minute cycle.
Does a nap make up for lost sleep?
Partly. A nap restores alertness well but does not reproduce the full structure of a night, particularly the long REM periods in the later cycles. It is a good supplement and a poor substitute.