Sleep Cycle Bedtime Calculator (90-minute REM cycles)

Find the best bedtimes (or wake times) that line up with complete 90-minute sleep cycles, plus the NSF-recommended total nightly sleep for your age.

Mode
Default 14 (Ohayon, Sleep 2017).
Age band (NSF recommendations)
Suggested bedtimes
6 cycles · 9 hours
Within NSF target 7–9h
9:46 PM
5 cycles · 7.5 hours
Within NSF target 7–9h
11:16 PM
4 cycles · 6 hours
Outside NSF target 7–9h
12:46 AM

Method: 90-min cycle approximation + sleep latency offset. Total-sleep ranges per Hirshkowitz M et al., Sleep Health 2015 (National Sleep Foundation expert consensus). Sleep latency default per Ohayon MM et al., Sleep 2017. Cycle length varies 70–120 min individually — treat as a planning estimate, not a precision tool. For persistent sleep problems, CBT-I per AASM 2021 clinical practice guideline.

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About this tool

Adult sleep architecture cycles every 90–110 minutes through four stages: N1 (drowsy transition), N2 (light sleep), N3 (slow-wave deep sleep), and REM. Waking at the end of a cycle (light N2 or just after REM) feels notably refreshed compared to waking mid-cycle (especially mid-N3). The standard planning heuristic — used by Sleep Foundation, NHS, and most consumer sleep apps — is to count back from target wake time in 90-minute increments. Adding 14 minutes for average sleep latency (per Ohayon MM et al., Sleep 2017, the time to fall asleep) gives target bedtimes. National Sleep Foundation 2015 recommendations (Hirshkowitz M et al., Sleep Health 2015) by age: newborn (0–3 mo) 14–17 h; infant (4–11 mo) 12–15 h; toddler (1–2 y) 11–14 h; preschool (3–5 y) 10–13 h; school-age (6–13 y) 9–11 h; teen (14–17 y) 8–10 h; young adult (18–25 y) 7–9 h; adult (26–64 y) 7–9 h; older adult (65+) 7–8 h. The 90-min cycle is an average — individual cycles vary 70–120 min and tend to lengthen across the night, so 5 cycles ≠ exactly 7.5 hours for everyone, but it is a useful planning approximation.

How to use it

  • Pick a mode: when should I go to bed if I need to wake at X, or when should I wake if I sleep at Y.
  • Enter the target time. Adjust your average sleep latency (14 min default).
  • See 4, 5, and 6-cycle options.
  • Compare total sleep to the NSF-recommended range for your age.

Frequently asked questions

Is the 90-minute cycle real?
Yes, but it is an average. Actual cycles range 70–120 min and lengthen across the night (REM proportion grows). The number is most reliable for the first 2–3 cycles after sleep onset.
Should I cut sleep short to wake at a cycle boundary?
No — total sleep matters more than cycle-aligned waking. Use cycle math to choose between 7 vs 7.5 hours, not to drop from 7.5 to 6.0.
Why add latency?
You do not fall asleep instantly. Mean sleep latency in healthy adults is ~14 min (Ohayon Sleep 2017). Subtract that from your bedtime to actually start the first cycle at the target time.
What if I have insomnia?
CBT-I (Cognitive Behavioral Therapy for Insomnia) is first-line for chronic insomnia per AASM 2021 clinical practice guideline. Sleep math alone will not fix insomnia.
Is data sent anywhere?
No. All math runs in your browser.

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