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 Bad to Sleep After a Workout? Napping After Exercise, ExplainedNo. Sleeping or napping after a workout is fine and may help you feel recovered. Keep naps to 20 or 90 minutes and finish them by mid-afternoon.4 min read
- How to Stay Awake While Driving (and When to Stop Trying)Pull over somewhere safe, have caffeine and take a 20-minute nap. Window-down and loud-radio tricks don't work reliably. Warning signs and a road-trip plan.5 min read
- Why Do I Feel Worse After a Nap? Sleep Inertia and How to Wake Up ClearYou likely woke from deep sleep. That groggy feeling is sleep inertia, and it usually fades within 30 minutes. How to nap and wake up without it.4 min read
More free sleep tools
All completely free, no sign-up.
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- 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.
- Kids Bedtime CalculatorThe right bedtime for your child's exact age and wake-up time.
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- Daylight Saving Time Sleep PlannerA day-by-day plan to shift your sleep before the clocks change.
- Sleep Schedule MakerA full daily timeline from your wake-up time: light, coffee, dinner, wind-down.
- Caffeine Limit CalculatorHow much caffeine you can have today, and how much is left.
- Sleep Deprivation QuizTen quick questions to see if you are running short on sleep.
- 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.