REM Sleep Calculator
REM sleep happens at the end of each roughly 90-minute sleep cycle, and each REM period is longer than the one before. That means most of your REM sleep comes in the last few hours of the night. Enter your bedtime to see when yours happens.
When will I be in REM sleep?
Enter your bedtime to estimate each sleep cycle and its REM period.
| Cycle | REM period (est.) | Wake up at | Total REM |
|---|---|---|---|
| 1 | 12:35 AM – 12:45 AM (10 min) | 12:45 AM · 1 h 30 min | 10 min |
| 2 | 2:00 AM – 2:15 AM (15 min) | 2:15 AM · 3 h | 25 min |
| 3 | 3:25 AM – 3:45 AM (20 min) | 3:45 AM · 4 h 30 min | 45 min |
| 4 | 4:50 AM – 5:15 AM (25 min) | 5:15 AM · 6 h | 1 h 10 min |
| 5 | 6:15 AM – 6:45 AM (30 min) | 6:45 AM · 7 h 30 min | 1 h 40 min |
| 6 | 7:40 AM – 8:15 AM (35 min) | 8:15 AM · 9 h | 2 h 15 min |
Highlighted rows give a full 7.5 to 9 hours of sleep. Times include 15 minutes to fall asleep and are estimates based on typical 90-minute cycles. Want to work backwards from an alarm instead? Use the sleep calculator.
What is REM sleep?
REM (rapid eye movement) sleep is the stage where most vivid dreaming happens. Your brain is nearly as active as when you're awake, while your body's muscles are temporarily relaxed so you don't act out your dreams. REM plays a big part in processing emotions and consolidating memories and new skills.
Each night you cycle through light sleep, deep sleep and REM about four to six times. Early cycles are dominated by deep sleep; later cycles carry longer and longer REM periods.
Why short nights cost you REM
Because REM periods grow through the night, the last cycle holds the longest one. Cut a 7.5-hour night down to 6 hours and you lose a fifth of your sleep, but nearly a third of your REM. If you need an early alarm, going to bed earlier protects your REM far better than sleeping in on the weekend. Running short most nights? Check your sleep debt.
More free sleep tools
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Nap Calculator
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Sleep Debt Calculator
How much sleep you owe from the past week, and how to pay it back.
Jet Lag Calculator
How long jet lag lasts and how to shift your sleep before you fly.
Sleep Efficiency Calculator
What share of your time in bed you actually spend asleep.
Frequently asked questions
How much REM sleep is normal?
For adults, REM usually makes up about 20 to 25 percent of total sleep. In a 7.5-hour night that is roughly 90 to 110 minutes, spread over four to six REM periods.
When does REM sleep happen?
At the end of each sleep cycle, roughly every 90 minutes. The first REM period starts about 70 to 90 minutes after you fall asleep and lasts only around 10 minutes; later ones get longer, so most REM happens in the last few hours before you wake up.
Is it bad to wake up during REM sleep?
Not really. REM is a light stage, so waking from it is fairly easy, and you are more likely to remember a dream. The groggy, heavy feeling usually comes from being woken out of deep sleep instead.
Can this calculator measure my REM sleep?
No. It estimates REM timing from typical 90-minute cycles. Your own cycles vary from night to night; wearables estimate sleep stages from movement and heart rate, and only a lab sleep study measures them directly.