REM sleep calculator
Enter the time you fall asleep to see roughly when your REM and deep sleep periods happen tonight, how much of each you'd get, and which alarm times avoid cutting off your longest REM period.
Your night
Estimates from the typical adult pattern (Carskadon & Dement). Only an overnight EEG (polysomnography) measures your real stages; wearables give rough guesses.
How much REM sleep do you need?
Healthy adults typically spend about 20–25% of their sleep in REM — roughly 90 minutes to 2 hours in a 7.5–9 hour night. No medical body sets a REM target; the share comes from sleep-lab studies of healthy sleepers, such as those summarised by the National Institute of Neurological Disorders and Stroke.
REM is weighted toward the end of the night. The first REM period may last around 10 minutes, the last can run 30 minutes or more. That's why cutting a night from 7.5 to 6 hours costs you a disproportionate share of REM.
How much deep sleep do you need?
Deep (N3, slow-wave) sleep is usually about 13–23% of the night in young and middle-aged adults — often 1 to 1.5 hours — and declines gradually with age. Most of it comes in the first two cycles, so an early bedtime protects it.
Getting more REM and deep sleep
- Sleep long enough. The simplest lever. A 7.5 or 9 hour night gives you the long late-night REM periods.
- Keep a regular schedule. A consistent wake time keeps REM timing aligned with your body clock.
- Go easy on alcohol near bedtime. It suppresses REM in the first half of the night.
- Check your caffeine. Caffeine late in the day can reduce deep sleep; use the caffeine cutoff calculator.
Learn what each stage does on the sleep stages page, or pick a bedtime for your alarm with the bedtime calculator.
Questions people ask
How do you calculate REM sleep?
You can only estimate it without a sleep lab. This calculator assumes about 90-minute cycles, adds your time to fall asleep, and places REM at the end of each cycle, getting longer through the night, following the typical adult pattern.
How much REM sleep is normal?
About 20–25% of total sleep for healthy adults, which is roughly 1.5–2 hours in a full night.
When does REM sleep happen if I go to sleep at 11 pm?
With 15 minutes to fall asleep, the first REM period starts roughly 80–90 minutes later, around 12:30 am, and further REM periods follow about every 90 minutes, the longest between about 5 and 7 am.
How much deep sleep do you need?
There is no official target. In healthy adults deep sleep is commonly 13–23% of the night, often 1–1.5 hours, and it naturally decreases with age.
Is my smartwatch REM reading accurate?
Wearables estimate stages from movement and heart rate. Validation studies show they track total sleep reasonably but agree only moderately with polysomnography on individual stages.