Sleep calculator / Nap calculator
Nap Calculator
Get the right alarm time for a power nap or a full-cycle nap, so you wake up sharp instead of groggy.
- 100% free
- No sign-up
- No app
The two naps worth taking
The power nap (10–20 minutes). Short enough that you wake up before sliding into deep sleep. You get a boost in alertness without the heavy, drugged feeling afterwards. This is the best nap for most workdays.
The full-cycle nap (about 90 minutes). One complete sleep cycle, including deep sleep and REM. It takes a big chunk of the afternoon, but it can help after a short night, before a night shift, or before a long drive.
Why a 45-minute nap can feel worse than none
Around 30 to 60 minutes in, you're likely to be in deep sleep. Waking from deep sleep causes sleep inertia: grogginess, slow thinking and bad mood that can last up to half an hour. That's why the calculator skips that window.
Best time of day to nap
Early afternoon, roughly 1 to 3 PM, lines up with the natural dip in alertness most people feel after lunch. Napping late in the day eats into the sleep pressure you need to fall asleep at night, so the calculator warns you about late naps.
What about a "coffee nap"?
Some people drink a coffee right before a 20-minute nap. Caffeine takes around 20 minutes to kick in, so it lands just as you wake up. It's worth a try for an early-afternoon slump, but not late in the day. Check how long caffeine stays in your system.
Frequently asked questions
How long should a power nap be?
10 to 20 minutes of sleep. Add the few minutes it takes you to drift off when you set your alarm, which the calculator does for you.
Is a 1-hour nap good?
Often not. At about an hour you are likely in deep sleep, so waking up tends to leave you groggy. Go for 20 minutes or a full 90.
Can napping ruin my night sleep?
Long or late naps can. If you have trouble falling asleep at night, keep naps short and before mid-afternoon, or skip them for a while.
Related reading
- Is It Better to Sleep 1 Hour or Stay Up All Night?Short on time before an early flight or exam? Here's when a short sleep beats staying up, how long to sleep, and how to time the alarm.3 min read
- How to Nap at Work, in Your Car or on a BreakKeep it to 10 to 20 minutes, nap on your own break time, and time it for early afternoon. How to nap at work, in a car or on a shift, safely.4 min read
- Is a 90-Minute Nap Too Long?Not usually. A 90-minute nap covers one full sleep cycle, so you tend to wake refreshed. Take it early in the afternoon so it doesn't hurt tonight's sleep.3 min read
More free sleep tools
All completely free, no sign-up.
- Sleep CalculatorBest bedtime or wake-up time, based on 90-minute sleep cycles.
- Sleep Debt CalculatorHow much sleep you owe this week, and how to pay it back.
- Caffeine Cutoff CalculatorHow much caffeine is still in you at bedtime, and your latest cup.
- Sleep Needs by AgeRecommended hours for every age, from newborns to over-65s.
- Sleep Efficiency CalculatorWhat share of your time in bed you actually spend asleep.
- Shift Work Sleep CalculatorWhen to sleep and stop caffeine around any shift, including nights.
- Jet Lag CalculatorDays to adjust, plus a shift-before-you-fly schedule.
These results are general estimates, not medical advice. Everyone's sleep is a little different. If you're often exhausted despite enough time in bed, snore loudly, or have been told you stop breathing in your sleep, see a doctor.