How to nap without ruining your night

A good nap is a short one, with the alarm set for 20 to 40 minutes. It should come 8 to 10 hours before you go to bed, so count back from your bedtime to find your window. If you go to bed at 10, that's 12 to 2, which is about when the after-lunch slump sets in anyway. If you go to bed at 11, it's 1 to 3.

A nap isn't necessary, but if you're fading in the afternoon, that's the time to take one. Set the alarm before you close your eyes, so the time it takes you to fall asleep counts toward the nap. When it goes off, get up, even if you never fell asleep, because lying there longer only pushes the nap later.

Why a late nap keeps you up at night

Every time you sleep, even for a nap, you use up some of the sleep pressure you've built up since you woke ¹. With a 10 o'clock bedtime, a nap that ends at 1:40 leaves you more than 8 hours to build it back up. One that ends at 7 leaves you 3, so you'll probably be lying there wide awake at 10. Then you're short on sleep the next morning, fading again by the afternoon and reaching for another nap.

So if the window closes before you get the chance, I'd skip the nap that day and go to bed on time. You'll be tired that evening, and that's fine, since you're going to bed anyway.

How long should a nap be?

Mayo Clinic puts the ideal nap at 20 to 30 minutes, and says to try not to go past 30 on a regular basis ². Aim for about that much actual sleep. Your alarm counts from the moment you lie down, though, and it can take a while to drop off, so I'd let it run past 30, but never past 40.

A short nap usually won't change how well you sleep that night, but long naps or a lot of them might ². The longer you nap, the more likely you are to wake up groggy too ².

You get some of that heavy, slow feeling any time you wake up ¹. Most of it lifts within 15 to 30 minutes, though it can take an hour or more before you feel completely normal. It's worse after a short night, or when you wake at a time you'd usually be asleep ¹.

Young adults who didn't usually nap had slept only about 5 hours the night before, and 10 minutes asleep perked them up straight away ³. Thirty minutes left them groggy and slower at first, then helped once that wore off ³. Those were minutes of actual sleep, which is less than the time on the alarm. Cut back to 20 if a 40-minute nap leaves you foggy for the rest of the afternoon.

If you can't nap at work

A nap goes best somewhere quiet and dark, at a comfortable temperature, with the TV off and your phone out of reach ². Most jobs don't come with anything like that. But if you get a lunch break and your car is in the lot, you can nap in it. Recline the seat, put on an eye mask and some earplugs, and set the alarm for 20 minutes. Give yourself some time to wake up before you're due back ², because the fog can take a while to lift.

If you drink coffee in the afternoon anyway, have it right before you lie down, as long as that's by about 2 if you go to bed at 10. Before a short nap of about 20 minutes, caffeine can take the edge off the grogginess when you wake up ¹. If you wait until after the nap, it kicks in too late to help with the worst of it ¹.

If your lunch break comes before your window opens, which can happen with a later bedtime, see whether you can take lunch a little later on the days you want a nap. And with nowhere at all to lie down, naps are for your days off.

When a nap is worth it, and when to skip it

A nap is worth it on the days you're fading, or on the afternoon before a long shift that's going to cut your night short ². And if you like a short nap as part of your daily routine, that's reason enough ².

A late Saturday night is another good time for one. Still get up within an hour or so of your usual time on Sunday, instead of sleeping until noon. Then if you're dragging by the afternoon, take a longer nap in your window, with the alarm at the full 40 minutes. Give yourself a little extra time afterward to shake off the fog.

If you have trouble falling asleep or staying asleep at night, a nap might make that worse ². Leave naps alone for now and work on your nights first, and once you're sleeping better, see whether you still want one. Some people also have trouble sleeping during the day, or anywhere but their own bed ². There's no reason to force a nap that won't come.

Everything here assumes you sleep at night. On night shifts, the nap goes before you head in instead.