Nap Calculator

Why nap length matters more than most people think

Sleep moves through distinct stages every 90 minutes or so, and waking up in the middle of deep slow-wave sleep (which typically kicks in after about 30 minutes) causes sleep inertia — that groggy, worse-than-before-the-nap feeling that can last 30 minutes or more. The "good" nap lengths are the ones timed to catch you either before deep sleep sets in, or after a full cycle completes and you're back in lighter sleep.

The three lengths worth knowing

10-20 minutes ("power nap"): stays in light sleep the whole time, easiest wake-up, still measurably boosts alertness. 90 minutes: a full sleep cycle including REM, closest to a genuine mini-sleep with the least grogginess for a longer nap. The 30-60 minute range in between is the one to generally avoid — it's long enough to hit deep sleep but too short to complete the cycle back out of it.