Result
To wake at 7:00 AM fully rested
9:46 PM
9 hours sleep, 6 cycles — recommended for adults
- Bedtime for 9 h sleep (6 cycles)Asleep ~10:00 PM9:46 PM
- Bedtime for 7.5 h sleep (5 cycles)Asleep ~11:30 PM11:16 PM
- Bedtime for 6 h sleep (4 cycles)Asleep ~1:00 AM12:46 AM
- Bedtime for 4.5 h sleep (3 cycles)Asleep ~2:30 AM2:16 AM
- Sleep latency assumed14 min
- Adult target7–9 hours (5–6 cycles)
How to use this calculator
- If your alarm is fixed, use "Wake at" mode and pick the bedtime that fits your real schedule.
- If you control bedtime, use "Sleep at" mode to find an alarm-friendly wake time.
- Don't obsess over hitting the exact minute — ±15 min is fine; your cycle isn't metronomic.
- Consistency matters more than perfection. Same bed and wake time daily beats a random schedule.
About this tool
Sleep happens in roughly 90-minute cycles that move from light NREM down to deep slow-wave sleep and back up through REM. Waking at the end of a cycle (lighter sleep) feels much less groggy than waking mid-cycle. This calculator picks bedtimes or wake times that align with whole cycles, plus 14 minutes for the average time it takes to actually fall asleep. The 90-minute number is the population average — your real cycle length is anywhere from 70 to 110 minutes, so treat the suggested times as ±15 minute targets, not stopwatches. Most adults need 5–6 cycles (7.5–9 hours) for consistent good function.
Frequently asked
You're probably right. Cycle length varies 70–110 min between people. The 90-min default is a population average; if your tracker has good data on you, trust it.
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