Nap Calculator
Enter when you woke up, when you plan to sleep tonight, and when you could nap. You get the best window, the alarm to set for a 20-, 30- or 90-minute nap, and whether it will cost you tonight.
Best nap window
12:30 PM–3:30 PM
ideal around 1:30 PM, ~7 h after waking
Set alarm for
2:00 PM
20 min + 10 to fall asleep
Timing
Good window.
Good window.
Tonight
9 h to bed
Leaves enough sleep pressure for tonight.
Light sleep only; alertness without grogginess.
Nap window by wake-up time
| Woke at | Window opens (+6 h) | Ideal (+7 h) | Latest (+9 h) |
|---|---|---|---|
| 5:00 AM | 11:00 AM | 12:00 PM | 2:00 PM |
| 5:30 AM | 11:30 AM | 12:30 PM | 2:30 PM |
| 6:00 AM | 12:00 PM | 1:00 PM | 3:00 PM |
| 6:30 AM | 12:30 PM | 1:30 PM | 3:30 PM |
| 7:00 AM | 1:00 PM | 2:00 PM | 4:00 PM |
| 7:30 AM | 1:30 PM | 2:30 PM | 4:30 PM |
| 8:00 AM | 2:00 PM | 3:00 PM | 5:00 PM |
| 9:00 AM | 3:00 PM | 4:00 PM | 6:00 PM |
The three nap lengths
| Nap | Minutes | What happens | Use it for |
|---|---|---|---|
| Power nap | 20 | Light sleep only; alertness without grogginess. | An afternoon slump, a long drive, before a night shift. |
| Short nap | 30 | Edge of deep sleep; can leave you groggy for 20-30 min. | Rarely; if you can't do 20, do 90. |
| Full cycle | 90 | One complete cycle incl. deep and REM; wake at a light stage. | Real sleep debt, a missed night, or a split shift. |
Set the alarm for the nap length plus about 10 minutes to fall asleep. 1:30 PM plus 20 + 10 is a 2:00 PM alarm.
Why the afternoon dip exists
Two systems govern sleepiness: sleep pressure (adenosine), which rises steadily from waking, and the circadian alerting signal, which dips in the early afternoon regardless of lunch. Around seven hours after waking the two cross: enough pressure to fall asleep within minutes, a natural lull to do it in, and enough hours left before bed to rebuild pressure. That is the window in the table, and it is why the same 20 minutes at 5 p.m. leaves you wide awake at midnight.
Frequently Asked Questions
How long should a nap be?
Twenty minutes or ninety. Twenty keeps you in light sleep and you wake alert; ninety is one full cycle so you wake at a boundary. Thirty to sixty minutes is the worst option: you are pulled into deep sleep and woken from it, and the grogginess (sleep inertia) can last half an hour or more.
What is the best time to nap?
About seven hours after you woke up, which for a 6:30 riser is around 1:30 p.m. That is the circadian afternoon dip, when sleep pressure is high enough to fall asleep quickly but tonight is far enough away not to suffer. After about nine hours awake, a nap starts to eat into the night.
Will a nap ruin my sleep tonight?
A 20-minute nap before 3 p.m. almost never does. A 90-minute nap, or any nap after 4 p.m., pays down sleep pressure you needed for bedtime, and you will fall asleep later. If you have insomnia, the standard advice is no naps at all until the night is fixed.
What is a coffee nap?
Caffeine right before a 20-minute nap. Caffeine takes about 20 minutes to be absorbed, so it kicks in as you wake, and the nap clears some adenosine that caffeine would otherwise have to block. Two small studies found it beat either alone for alertness. It only works for the 20-minute version.
These calculators use published sleep-science guidelines and are for general guidance. They are estimates, not medical advice: persistent insomnia, loud snoring or gasping in sleep, or daytime sleepiness that affects driving are reasons to see a doctor, not to adjust a bedtime.