Recovery

The Science of Napping

A nap can leave you sharper for the rest of the day, or noticeably groggier — and the difference usually comes down to length and timing, not whether you napped at all.

Why nap length changes the outcome

Like nighttime sleep, naps move through the same sequence of stages, just compressed. A short nap stays in light sleep and skips deep sleep entirely, which is why it's easy to wake from. A longer nap has time to reach deep, slow-wave sleep — more physically restorative, but far harder to wake out of cleanly, producing the groggy, disoriented feeling known as sleep inertia.

Common nap lengths and what research associates with each

• 10–20 minutes: a "power nap" that stays almost entirely in light sleep — quick alertness benefits with minimal grogginess on waking.
• ~26 minutes: the duration used in a well-known NASA study of pilots and astronauts, which found measurable improvements in alertness and performance at roughly this length.
• 45–60 minutes: long enough to reach deep sleep — more restorative for physical fatigue, but commonly followed by 15–30 minutes of grogginess after waking.
• ~90 minutes: long enough to complete a full sleep cycle including REM. Waking at the end of a complete cycle, rather than partway through one, tends to avoid the worst of the grogginess despite the longer duration.

Best time of day to nap

Early-to-mid afternoon — roughly 1 to 3 PM for someone on a typical daytime schedule — tends to align with a natural dip in alertness driven by the circadian rhythm, making it easier to fall asleep quickly without needing to be especially tired. Napping too late in the afternoon or evening risks reducing sleep drive for the coming night, making it harder to fall asleep at your usual bedtime.

Try the nap calculator to see the exact wake-up time for each nap length from right now or a chosen start time, or check the sleep debt tracker if you're trying to figure out how much catching up you actually need.