SleepCycleCalcNap Calculator
A nap's value depends almost entirely on its length. Twenty minutes keeps you in light sleep and wakes you refreshed; ninety minutes completes a full sleep cycle. The awkward middle — waking from deep sleep at 40–60 minutes — is where nap regret lives. Enter when your nap starts and get both good options.
Leave the start time empty and press “Nap starts now” to use the current time on your device.
The 20-minute power nap
Twenty minutes is enough for stage N1 and N2 light sleep, which is where the alertness benefit lives, and short enough that you surface before deep sleep starts. Most people wake from a power nap clear-headed within a few minutes. It is the right choice on a workday: short, schedulable, and it does not steal sleep pressure from the night ahead. The main skill is actually stopping at 20 — set the alarm when you lie down, counting the fall-asleep buffer.
The 90-minute full-cycle nap
Ninety minutes takes you through a complete cycle — light, deep, and REM sleep — so you wake from light sleep at the end rather than being dragged out of the deep middle. It is the better choice when you are genuinely sleep-deprived, studying or doing creative work (REM is linked to consolidating and connecting ideas), or covering for a short night ahead. The cost is time, and a stronger effect on that night's sleep if taken late.
Why 40–60 minutes feels terrible
That window is typically spent in deep N3 sleep. An alarm there produces the strongest sleep inertia of the day — worse, briefly, than no nap at all. If you only have an hour, the unintuitive but reliable advice is to take the 20-minute version and spend the remaining time awake, in daylight, rather than "using the whole hour".
Frequently asked questions
Is a 20-minute or 90-minute nap better?
They do different jobs. A 20-minute power nap stays in light sleep, so you wake clear-headed — best for an afternoon alertness boost. A 90-minute nap completes a full cycle including deep and REM sleep, so you wake clear-headed too but get more restoration — better for learning, creativity, or covering a genuinely short night. The nap to avoid is 40–60 minutes: long enough to reach deep sleep, too short to finish it.
What is the best time of day to nap?
Early to mid-afternoon, roughly 1–3 PM for a typical schedule, matches the natural post-lunch dip in alertness and is least likely to interfere with night sleep. Napping after about 4 PM borrows sleep pressure from the night ahead.
Should the nap calculator include falling-asleep time?
Yes. The tool adds a short buffer (10 minutes by default for naps) before the nap itself starts, because the 20 or 90 minutes only count once you are actually asleep. If you are a slow napper, raise it.
Do naps count toward my daily sleep need?
Partly. A 90-minute nap is a real cycle and does reduce sleep debt somewhat; a 20-minute nap mostly restores alertness rather than repaying debt. Neither fully substitutes for a proper night — see the sleep debt calculator for the weekly picture.