Sleep Time Calculator
Find the best times to go to bed based on when you need to wake up, using 90-minute sleep cycles.
- Free to use
- Accurate results
- No registration required
- Works on all devices
Enter your wake-up time to see suggested bedtimes based on 90-minute sleep cycles.
Use 24-hour HH:MM format, e.g. 07:00 or 06:30.
Your result
23:15
5 cycles (7.5 hours)
6 cycles (9 hours)21:45
4 cycles (6 hours)00:45
3 cycles (4.5 hours)02:15
AI explanation
Formula
Bedtime = wake-up time − minutes to fall asleep − (90 minutes × number of sleep cycles)Worked example
Wake-up 07:00, 15 minutes to fall asleep
| Field | Value |
|---|---|
| Wake-up time (24-hour) | 07:00 |
| Minutes to fall asleep | 15 |
| 6 cycles (9 hours) | 21:45 |
| 5 cycles (7.5 hours) | 23:15 |
| 4 cycles (6 hours) | 00:45 |
| 3 cycles (4.5 hours) | 02:15 |
Assumptions
- Assumes an average sleep cycle length of 90 minutes, a commonly cited approximation — actual individual cycle length varies.
- Falling asleep at the end of a suggested bedtime, then waking naturally at the end of a full cycle, is generally associated with feeling more rested, though individual results vary.
Frequently asked questions
Which bedtime option should I pick?
5-6 cycles (7.5-9 hours of sleep) is the commonly recommended range for adults, so those options are highlighted, but individual sleep needs vary.
I have a fixed bedtime and want to know when to wake up instead — is there a version for that?
Yes — see the Wake Up Time Calculator, which works forward from a bedtime instead.
Why do the bedtime options seem to wrap to "the previous day"?
Since bedtimes are naturally before a wake-up time, they're shown as ordinary clock times without a date — read them as "the night before" your wake-up time.