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Nap calculator

Pick when you will lie down and how long you want to sleep. You get the alarm time, the sleep stage you are likely to reach, and how the nap sits against tonight's bedtime.

Updated October 3, 2026 · NASA 1995 · Brooks & Lack 2006 · Tassi & Muzet 2000

Set the alarm for:

Adds 15 minutes to fall asleep. Grogginess ratings from the studies above. How we calculate

Nap length versus grogginess on waking
10 mingrogginess: minimal20 mingrogginess: low26 mingrogginess: low to moderate30 mingrogginess: moderate45 mingrogginess: moderate to high60 mingrogginess: high90 mingrogginess: low

Sleep inertia ratings from the cited studies · as of October 3, 2026

How to read the result

Ten to twenty-six minutes keeps you in light sleep, which is why those lengths refresh without grogginess — in the NASA study a 26-minute average nap improved reaction-time performance by 34% and alertness by 54%. Thirty to sixty minutes usually ends inside deep sleep, where waking produces sleep inertia for ten to thirty minutes. Ninety minutes is a full cycle and tends to end in light sleep again. The "awake before bed" figure uses an eight-hour rule of thumb from sleep-hygiene guidance; it is a planning number, not a measured threshold.

Every length and start time also has its own page: nap lengths and times →

Sources

  1. A brief afternoon nap following nocturnal sleep restriction: which nap duration is most recuperative? — Sleep 29(6):831-840, 2006 (Brooks A., Lack L.)
  2. Alertness Management: Strategic Naps in Operational Settings — NASA Technical Memorandum 108839 (Rosekind M.R. et al.), 1995; also J Sleep Res 4(S2):62-66
  3. Sleep inertia — Sleep Medicine Reviews 4(4):341-353, 2000 (Tassi P., Muzet A.)
  4. Brain Basics: Understanding Sleep — NINDS (NIH)

General information from population studies (NIH, CDC, NSF, AASM). It is not medical advice and does not replace a clinician who knows you.