How the sleep calculator works
Sleep runs in cycles of roughly 90 minutes, moving from light sleep to deep sleep to REM. Waking at the end of a cycle, during light sleep, tends to feel easier than being pulled out of deep sleep.
Example: to wake at 7:00 AM after five cycles, allowing 15 minutes to fall asleep, go to bed at 11:15 PM.
Cycle length varies from person to person and through the night, from about 70 to 120 minutes, so use these times as a starting point and adjust to what works for you. If you are regularly tired despite enough sleep, talk to a doctor.
Bedtime chart
When to get into bed for 4, 5 or 6 full cycles, allowing 15 minutes to fall asleep:
| Wake at | 6 cycles (9 hr) | 5 cycles (7.5 hr) | 4 cycles (6 hr) |
|---|---|---|---|
| 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 |
Most adults do best with five or six cycles. Four cycles works for an occasional short night, but not as a habit.
Next steps
Shift work or travel? The time zone converter helps when you're planning sleep across time zones.
Frequently asked questions
How many hours of sleep do adults need?
Most adults need 7 to 9 hours a night, according to sleep medicine guidelines. Teenagers need 8 to 10.
Is 6 hours of sleep enough?
For most people, no. Four cycles (6 hours) is fine occasionally, but regularly sleeping under 7 hours is linked to poorer health and concentration.
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