When should you sleep?
Sleep moves through roughly 90-minute cycles. Timing your alarm to the end of a cycle — instead of the middle — helps you wake up feeling refreshed rather than groggy.
To wake up at 7:00 AM, head to bed at one of these times:
Highlighted options hit the recommended 7–9 hours for a adult (18–64). A ~15 min buffer to fall asleep is included.
The science of sleep cycles
The recommendations above are built from a few well-established ideas about how we sleep.
~90-minute cycles
A full cycle runs about 90 minutes, cycling through light sleep, deep sleep and REM. A typical night is 4–6 of them.
Wake between cycles
Waking at the end of a cycle, rather than mid-cycle, leaves you feeling alert. Waking during deep sleep is what causes grogginess.
A buffer to drift off
Most people take around 15 minutes to actually fall asleep, so that buffer is added to every estimate.
How much sleep you need
National Sleep Foundation guidance by age group.
- Teenager (14–17)
- 8–10 hours
- Adult (18–64)
- 7–9 hours
- Older adult (65+)
- 7–8 hours
Guidance only — individual needs vary. This tool is not medical advice.