If your morning alarm is set for 4:00 AM, the bedtime that will leave you feeling most refreshed depends on two numbers most calculators ignore: your personal cycle length (somewhere between 75 and 115 minutes) and your typical sleep onset latency (how long it takes you to actually fall asleep).
| Your cycle length | Go to bed at | Total sleep | Cycles |
|---|---|---|---|
| 80 min | 9:08 PM | 6h 40m | 5 |
| 85 min | 8:43 PM | 7h 5m | 5 |
| 90 min | 8:18 PM | 7h 30m | 5 |
| 95 min | 7:53 PM | 7h 55m | 5 |
| 100 min | 7:28 PM | 8h 20m | 5 |
Each row assumes a 12-minute sleep onset latency. If you fall asleep faster or slower than that, adjust the bedtime by the difference.
Every number on this page assumes you\u2019re an average sleeper. You probably aren\u2019t. Our 2-minute calculator gives you the exact bedtime that matches your cycle length — not the generic 90-minute assumption.
Start the calibration→The right bedtime depends on your personal cycle length. For a 90-minute sleeper, go to bed roughly 7 hours 42 minutes before 4:00 AM (5 cycles + 12 min onset). For an 80-min sleeper, the window shifts earlier; for a 100-min sleeper, later. See the table above for exact times.
Only if the later wake time aligns better with your cycle length. An extra hour of mid-cycle sleep often feels worse than the "shorter" alternative that wakes you cleanly at a cycle boundary.
Most adults feel best at 5 complete cycles — roughly 6.5 to 8.3 hours depending on your individual cycle length. Four cycles is the short-sleeper floor; six cycles is for adolescents and recovery nights.