Wake-up times by sleep cycle
Each cycle is 90 minutes; a 15-minute sleep-onset latency is included. Times marked “next day” fall after midnight.
| Cycles | Sleep duration | Wake time |
|---|
Why you wake up groggy (sleep inertia)
That heavy, foggy feeling right after waking has a name: sleep inertia. It happens when an alarm pulls you out of deep, slow-wave sleep. During deep sleep your brain slows down dramatically, so being yanked out of it leaves you disoriented and slow for anywhere from a few minutes to half an hour or more.
Sleep inertia is most severe when you wake from deep sleep, which is concentrated in the first half of the night. By aiming your alarm at the end of a 90-minute cycle — when you are in light sleep or briefly awake — you minimise the amount of deep sleep you disturb and wake up far more easily. This is exactly what the wake-up times above are designed to do.
For the reverse question — what time should you go to bed to wake up at a specific hour — use the bedtime calculator. You can also start from the main calculator, which handles both directions.
A few habits also reduce morning grogginess: keep a consistent schedule, expose yourself to daylight soon after waking, and avoid hitting snooze, which only fragments the light sleep you do get.