Nap Calculator
Tells you when to set an alarm for a nap, and how late you can nap without affecting tonight’s sleep.
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The formula
alarm = nap start + time to fall asleep + nap length latest finish = bedtime − 8 hours
The 8-hour gap is a rule of thumb, not a measured limit. It matches the usual advice to nap before mid-afternoon if you go to bed at around 23:00.
What to watch out for
Short naps of 10 to 20 minutes tend to lift alertness with little grogginess. Longer ones reach deeper sleep, which can leave you groggy for a while on waking, known as sleep inertia.
Early afternoon suits most people, when alertness naturally dips. People who work shifts may need to nap at other times. If you need a nap most days despite a full night’s sleep, it is worth raising with a doctor.
Frequently Asked Questions
What time should I wake from a nap at 14:00?
Allowing 5 minutes to fall asleep, 14:25 for a 20-minute nap, or 15:35 for 90 minutes.
How late can I nap?
A rough guide is to finish at least 8 hours before bed. For a bedtime of 23:00 that means by 15:00, and for 22:00 by 14:00.
Does a nap make up for a short night?
It helps with alertness and can ease sleepiness for a few hours, but it does not fully replace a proper night’s sleep.