HesperaFree web tool · no sign-up
Nap calculator: the right length at the right hour.
Tell it when the nap starts. It gives you two alarm times — a 20-minute power nap and a full 90-minute cycle — checks whether you’re in your natural afternoon dip, and warns you before a nap starts stealing from tonight.
Set the alarm for
- 2:00 PMPower nap · 20 min (+10 to drift off)light sleep only — you wake up sharp, no grogginess
- 3:10 PMFull cycle · 90 min (+10 to drift off)one complete cycle incl. deep and REM — for a bad night behind you
Avoid the 30–60 minute middle: that’s when you wake from deep sleep feeling worse than before. Naps are on top of, not instead of, tonight.
The logic
What this nap calculator actually does.
- 01
Find the dip, not a random gap
Body temperature and alertness sag roughly 6–8 hours after you wake — the classic post-lunch dip. A nap placed there falls asleep faster and disturbs the night least.
- 02
Two lengths that work
20 minutes buys alertness with zero grogginess. 90 minutes buys a full cycle including deep and REM sleep. Everything in between — the accidental 30–60 minute nap — tends to wake you mid-deep-sleep, which is why the calculator only offers these two.
- 03
Add the drift-off buffer
Nobody falls asleep the second they lie down. The calculator adds about ten minutes before starting the clock, so a "20-minute nap" sets the alarm 30 minutes out.
- 04
Protect tonight
A long nap too close to bedtime drains the sleep pressure you need to fall asleep at night. The calculator flags naps that land inside that danger zone.
Quick reference
Nap lengths, compared.
| Nap length | What you get | Waking up feels | Best for |
|---|---|---|---|
| 10–20 min | Light sleep only | Alert almost immediately | Any afternoon dip, even a work break |
| ~30 min | Slips into early deep sleep | Often groggy for a while | Honestly? Avoid this length |
| ~60 min | Mostly deep, slow-wave sleep | Some grogginess, then sharp | Learning-heavy days, real sleep debt |
| ~90 min | One complete cycle incl. REM | Usually clean, at a cycle end | Bad night behind you, free afternoon |
Planning tonight too? Use the bedtime sleep calculator — a nap this afternoon changes the answer.
Naps in context
A nap changes tonight. The app does that math.
The web calculator treats today as average. The Hespera app (iPhone and Android) logs the nap alongside caffeine, stress and exercise, then moves tonight’s lights-out target and wake window to match — and shows you, over weeks, whether napping actually helps your nights.
FAQ
Nap questions, answered.
How long should I nap?
For most situations, 10–20 minutes. That keeps you in light sleep, so you wake up alert instead of groggy. Go to 60 minutes if you need deep sleep after a short night, or 90 minutes for a complete cycle — and avoid the 30–45 minute middle ground, which tends to wake you from deep sleep at its worst.
What is the best time of day to nap?
Roughly 6 to 8 hours after you woke up, which for a 7 AM riser means about 1–3 PM. That window sits on the natural circadian dip, so you fall asleep faster, and it leaves enough hours before bedtime for sleep pressure to rebuild.
Will napping ruin my sleep at night?
A short nap in the early afternoon usually doesn’t. Naps become a problem when they are long, late, or both — a 90-minute nap at 6 PM removes exactly the sleep pressure you need at 11 PM. Keep long naps at least 8 hours before bedtime.
Why do I feel worse after a nap?
That heavy, disoriented feeling is sleep inertia — you were woken from deep sleep. It usually means the nap ran 30–60 minutes, long enough to enter slow-wave sleep but not long enough to finish the cycle. Shorten the nap to 20 minutes or extend it to a full 90.
What is a coffee nap and does it work?
Drink a coffee, then immediately nap for 15–20 minutes: the nap clears some adenosine while the caffeine is still being absorbed, and both effects land together when you wake. Small studies on drivers found it beats either coffee or a nap alone. It only makes sense early in the day — that caffeine still counts against tonight.
How does the Hespera app handle naps?
You log the nap like any other factor of your day, and the app folds it into tonight’s plan — moving your lights-out target and wake window rather than pretending the nap didn’t happen. Over time it shows whether napping helps or hurts your nights.