Nap Calculator
Updated for 2026 · All math runs privately in your browser
A 20-minute nap refreshes you. A 45-minute nap wrecks you. Pick a length and see exactly which sleep phases you'll hit on the ring — plus your ideal alarm time.
Your nap
Drag it and watch the ring: green zones refresh, the red zone groggy-fies.
Defaults to right now. We add ~10 minutes to drift off.
Your nap plan
Nap phase ring
- Nap length—
- Falling asleep~10 min
- Deepest phase reached—
- Wake-up call—
Nap in the early afternoon (1–3 PM) when your energy naturally dips. Late naps steal your nighttime sleepiness.
How to use this calculator
- Choose your nap length — try 20 minutes for the classic power nap.
- Set when the nap starts (defaults to now).
- Check the ring: the marker shows where you'll wake. Green zones = refreshing, red = groggy.
- Set your alarm for the suggested time and put the phone across the room.
How the math works
Alarm time = start time + ~10 minutes to fall asleep + nap length. The 10-minute drift-off is the average sleep latency for a daytime nap.
The ring maps a 90-minute sleep cycle: light sleep (0–20 min), deep sleep (20–60 min) and REM (60–90 min). Waking from light sleep or at the full-cycle boundary feels clean; waking from deep sleep triggers sleep inertia.
The zones: 10–20 min = power nap (light sleep only) · 30–60 min = grogginess zone (deep sleep) · 90 min = full cycle, the other sweet spot.
Frequently asked questions
20 minutes for a classic power nap, or 90 minutes for a full sleep cycle. Lengths between 30 and 60 minutes tend to end in deep sleep, which causes grogginess — the infamous nap hangover.
A 10–20 minute nap that keeps you in light sleep. You wake up before deep sleep begins, so you get a boost in alertness and mood without sleep inertia.
Around 30–60 minutes in, you sink into deep slow-wave sleep. Waking from deep sleep triggers sleep inertia — grogginess and confusion that can take 30+ minutes to clear, wiping out the nap's benefit.
Not if you can spare it: 90 minutes is one full sleep cycle (light → deep → REM), so you wake at a natural boundary feeling refreshed. Just take it early in the afternoon so it doesn't push your bedtime later.
Early afternoon, roughly 1–3 PM, when your circadian rhythm naturally dips. Napping after 4 PM can make it harder to fall asleep at night.
Drink a coffee, then nap for 20 minutes immediately. Caffeine kicks in right as you wake, and the combination has been shown in studies to beat either coffee or napping alone for alertness.