Nap Calculator
Plan the perfect nap to boost energy without waking up feeling worse.
Select your nap parameters to see when you should wake up.
How this calculator works
A nap works differently depending on how long it lasts. Sleep runs in cycles of roughly 80 to 100 minutes, and where you are in that cycle when you wake up affects how you feel afterwards (NHLBI).
A short nap keeps you in lighter sleep, so waking is usually easy. A longer nap takes you into deep sleep, where waking tends to feel heavy and disoriented — an effect known as sleep inertia. A full cycle brings you back out the other side.
This calculator adds a short buffer for the time it takes to fall asleep, then works forward to the wake time that fits the nap type you chose.
Choosing a nap length
About 20 minutes. Short enough to stay in light sleep for most people. The usual choice when you need to function again soon afterwards.
About 60 minutes. Long enough to reach deep sleep. Waking from this point often feels worse before it feels better, so it suits situations where you have time to shake it off.
About 90 minutes. Roughly one full cycle, ending closer to light sleep again. Often chosen when there is time for a proper nap.
These are planning conventions, not rules. Cycle length varies between people and across the day, so treat the result as a starting point and adjust based on how you actually feel.
Napping without disrupting your night
Napping later in the day, or for longer stretches, can make falling asleep at night harder. If you are already struggling with night-time sleep, an earlier and shorter nap is generally the safer choice.
General sleep guidance also notes that keeping a consistent sleep and wake schedule supports better sleep overall (CDC).
Common questions
Why do I feel worse after a long nap?
Waking from deep sleep produces sleep inertia — a groggy, heavy feeling that can last a while. It usually passes, but it is the main reason short naps are often preferred when you need to be alert soon after.
Is napping bad for you?
For most people it is simply a tool. It becomes a problem mainly when it displaces night-time sleep. If you find yourself needing long naps regularly despite sleeping enough at night, that is worth raising with a healthcare professional.
Does a nap replace lost night-time sleep?
Not fully. A nap can reduce how tired you feel in the short term, but it is not a substitute for consistent night-time sleep.
Related guides
Sources
General information about sleep stages and cycles is based on published guidance from the National Heart, Lung, and Blood Institute (NIH). Sleep duration recommendations are based on guidance from the CDC.