How to choose a wake-up time
- "I'm going to bed at…" is selected. Enter your bedtime, or choose Sleep now.
- Set how long you usually take to fall asleep.
- Pick an alarm time from the list: five or six cycles give 7.5 to 9 hours of sleep.
Why waking between cycles helps
Sleep runs in cycles of roughly 90 minutes, moving from light sleep into deep slow-wave sleep and then REM sleep. When an alarm goes off during deep sleep, you are more likely to wake up groggy and disoriented, a state called sleep inertia that can last 15 to 30 minutes. Timing the alarm for the end of a cycle, when sleep is lighter, often makes waking easier.
Cycle length varies between people and through the night, so if you often wake a few minutes before the alarm, your cycles may be shorter: try the 80-minute option. Getting enough total sleep matters most: adults need 7–9 hours. Keeping the same wake-up time every day, including weekends, also stabilises your body clock. The calculator runs in your browser.
ℹ️ Not medical advice: an estimate for healthy adults. Ask a doctor or qualified professional about your own situation.
FAQ
What time should I wake up if I sleep at 11 pm?
With 15 minutes to fall asleep: 6:45 am (5 cycles) or 8:15 am (6 cycles).
Is 4.5 hours of sleep enough?
Three cycles may feel better than 5 hours of broken sleep, but it is not enough on a regular basis.
Do smart alarms work the same way?
Yes, they try to wake you in light sleep within a time window, using movement.