Sleep cycle calculator
Work backwards from the roughly 90-minute sleep cycle: give a wake time and get the bedtimes 3–6 cycles earlier, or give a bedtime and get the wake times, including the default 14-minute sleep latency (adults average 10–20 minutes) and flagging the recommended 5-cycle, 7.5-hour option inside the AASM 7–9 hour band.
Runs in your browserEvery computation happens in your browser — your data never leaves this device.
Sleep settings
Cycle length varies from person to person (70–120 minutes), so treat these times as guidance, not to the minute.
Result
Enter a time, then press “Calculate sleep times”.
What this tool does
- If you wake at 7:00 and never feel rested, the 23:16 bedtime for five cycles turns “go to bed earlier” into an actual time.
- After a late night, start from the moment you can actually lie down and read off the 3-cycle (4.5 h) and 4-cycle (6 h) wake times, so the alarm misses deep sleep.
- When travelling across time zones, recompute your sleep points in local time instead of forcing your home schedule.
- Compare cycle lengths of 80, 90 and 100 minutes to find the one that matches how you actually feel.
Example
Input
Wake time 07:00, sleep latency 14 minutes, cycle length 90 minutes
Output
6 cycles (9 h) → 21:46; 5 cycles (7 h 30 min) → 23:16 (recommended); 4 cycles (6 h) → 00:46; 3 cycles (4 h 30 min) → 02:16
23:16 comes from going back five cycles and adding the 14-minute latency: 07:00 − 14 min − 5 × 90 min.
Frequently asked questions
Why subtract 14 minutes for falling asleep?
Lying down is not the same as being asleep. Adults average 10–20 minutes to fall asleep and this tool defaults to 14. If you drop off instantly, set it to 5; if you toss and turn, 20 is closer to reality.
Is a 90-minute cycle reliable?
Ninety minutes is a population average; individuals run 70–120 minutes, and cycles vary within a single night too. Treat it as a rough way to avoid waking in deep sleep rather than a precision alarm.
Is six hours really worse than seven and a half?
For most adults the AASM and National Sleep Foundation recommend 7–9 hours, and 7.5 hours sits mid-band while landing on whole cycles, which is why it is flagged as recommended. Habitual six-hour nights build up sleep debt; the occasional short night is not a problem.
How does this apply to naps?
Keep a short nap under 20 minutes so you do not wake out of deep sleep with grogginess; if you want a full cycle, plan around 90 minutes. This tool is not tuned for naps.
What does the “Next up” marker mean?
It reads the time you opened the page and highlights the closest option that has not happened yet, so you can act on it directly. That calculation happens locally and is never uploaded.
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