The three nap lengths that work
Naps come in roughly three useful sizes. A power nap of 10–20 minutes keeps you in light sleep — you wake quickly with a noticeable boost in alertness, attention and mood. A recovery nap of about 30 minutes adds some deeper sleep; you trade a little grogginess for genuine recovery after a poor night. A full-cycle napof 90 minutes completes a whole sleep cycle and ends in lighter sleep again, so waking is easy and restoration is the most complete.
The nap length to avoid
Anywhere between roughly 45 and 80 minutes is the worst zone — you wake mid-deep-sleep, your brain takes 20–30 minutes to clear the fog, and you feel worse than before. If you can't fit a full 90-minute nap, keep it to 30 minutes or under.
When to nap
The natural afternoon dip in alertness, around 1pm–3pm, is the easiest window. Napping later than about 4pm starts to push back your night-time sleep, especially if it's longer than 20 minutes. If your evenings are already short on sleep, push the nap earlier or skip it.
The coffee nap trick
Drink a coffee right before lying down for a 20-minute nap. Caffeine takes about 20–30 minutes to reach peak effect, so it arrives just as your alarm goes off — combining the alertness boost of the nap with the kick of the caffeine. It only works for short naps, and only if you can actually fall asleep with caffeine in your stomach.