How the sleep cycle calculator works
During the night you move through repeating sleep cycles of roughly 90 minutes, each running from light sleep to deep sleep to REM. Waking at the end of a cycle — in light sleep — feels natural and refreshed. Waking in the middle, especially out of deep sleep, causes sleep inertia: that heavy, groggy feeling. This calculator counts back (or forward) in 90-minute blocks, plus the time it takes you to fall asleep, to land your alarm between cycles.
How many cycles do you need?
- 5–6 cycles (7.5–9 hours) — the healthy target for most adults.
- 4 cycles (6 hours) — a workable minimum on a busy night.
- 3 cycles (4.5 hours) — short, for emergencies only; expect to feel it.
Bedtime chart: when to go to sleep
Find your wake-up time, then go to bed at one of these times so you wake at the end of a 90-minute cycle. Each time already includes 15 minutes to fall asleep. Six cycles is 9 hours of sleep, five is 7.5 hours — the two most adults should aim for.
| To wake at | Sleep at (6 cycles, 9 h) | Sleep at (5 cycles, 7.5 h) | Sleep at (4 cycles, 6 h) |
|---|---|---|---|
| 5:00 AM | 7:45 PM | 9:15 PM | 10:45 PM |
| 5:30 AM | 8:15 PM | 9:45 PM | 11:15 PM |
| 6:00 AM | 8:45 PM | 10:15 PM | 11:45 PM |
| 6:30 AM | 9:15 PM | 10:45 PM | 12:15 AM |
| 7:00 AM | 9:45 PM | 11:15 PM | 12:45 AM |
| 7:30 AM | 10:15 PM | 11:45 PM | 1:15 AM |
| 8:00 AM | 10:45 PM | 12:15 AM | 1:45 AM |
| 8:30 AM | 11:15 PM | 12:45 AM | 2:15 AM |
| 9:00 AM | 11:45 PM | 1:15 AM | 2:45 AM |
Wake-up chart: when to set your alarm
The other way round — if you're going to bed at a set time, wake at one of these.
| Going to bed at | Wake at (5 cycles, 7.5 h) | Wake at (6 cycles, 9 h) | Wake at (4 cycles, 6 h) |
|---|---|---|---|
| 9:00 PM | 4:45 AM | 6:15 AM | 3:15 AM |
| 9:30 PM | 5:15 AM | 6:45 AM | 3:45 AM |
| 10:00 PM | 5:45 AM | 7:15 AM | 4:15 AM |
| 10:30 PM | 6:15 AM | 7:45 AM | 4:45 AM |
| 11:00 PM | 6:45 AM | 8:15 AM | 5:15 AM |
| 11:30 PM | 7:15 AM | 8:45 AM | 5:45 AM |
| 12:00 AM | 7:45 AM | 9:15 AM | 6:15 AM |
| 12:30 AM | 8:15 AM | 9:45 AM | 6:45 AM |
| 1:00 AM | 8:45 AM | 10:15 AM | 7:15 AM |
Sleep better tonight
- Keep a consistent bed and wake time — even on weekends.
- No screens for 30–60 minutes before bed; keep the room dark and cool.
- Avoid caffeine after early afternoon and heavy meals late at night.
What time should I go to bed if I wake up at 6 AM?
Aim for 8:45 PM (6 cycles, 9 hours) or 10:15 PM (5 cycles, 7.5 hours). Both include 15 minutes to fall asleep and wake you between cycles.
What time should I sleep to wake up at 7 AM?
9:45 PM or 11:15 PM for a full night, or 12:45 AM if you only have 6 hours.
If I go to bed at 11 PM, when should I wake up?
Set your alarm for 6:45 AM (7.5 hours) or 8:15 AM (9 hours). Waking at the end of a cycle feels far better than being pulled out of deep sleep.
Is every cycle exactly 90 minutes?
No — 90 minutes is the average; yours may run 80–110. Treat the times as close targets, and notice which cycle count leaves you feeling best.
Why add "time to fall asleep"?
Because your cycles start when you actually drift off, not when your head hits the pillow. Most people take 10–20 minutes.
Is 6 hours enough?
It's a workable minimum for the occasional night, but most adults need 7–9 hours regularly for health, focus and mood.