[ ESTIMATES ONLY ]
Sleep Calculator.
Pick a wake-up time to find the best bedtimes — or a bedtime to find the best wake-up times — based on 90-minute sleep cycles.
No signup Not medical advice Works offline
Please read
This calculator gives estimates based on average ~90-minute sleep cycles. It is not medical advice — if you have ongoing sleep problems, please talk to a qualified health professional. Full disclaimer →
Calculate your sleep times
Recommended times
How the sleep calculator works
Sleep happens in cycles of roughly 90 minutes, moving through light sleep, deep sleep and REM sleep. Waking up between cycles — groggy and mid-cycle — feels worse than waking up at the natural end of one. This calculator plans your schedule so your anchor time lands at the end of a full cycle.
Wake-up time → bedtimes
Starting from your desired wake-up time, the calculator works backwards: subtract your sleep latency (the time you need to fall asleep) and then 4, 5 or 6 full cycles. Those become three recommended bedtimes.
Bedtime → wake-up times
The reverse: add your sleep latency, then 4, 5 or 6 full cycles, to get three recommended wake-up times. Any result past midnight is handled automatically.
Which one is best?
Adults typically need about 7–9 hours of sleep. With 90-minute cycles that points to 5 cycles (7h 30m) — marked as the best fit. Four cycles (6h) suit shorter sleepers; six cycles (9h) suit those who need more. Individual needs vary, so treat the times as a starting point, not a prescription.
How to use the sleep calculator
- Choose a mode: wake-up time → bedtimes or bedtime → wake-up times.
- Pick your anchor time, or press I'm going to bed now to use the current time.
- Adjust sleep latency (default 15 minutes) and cycle length (default 90 minutes) if you know your own patterns.
- Press Calculate and compare the 4-, 5- and 6-cycle recommendations — the 5-cycle option is marked as the best fit.
Worked example
Wake-up time of 7:00 AM with a 15-minute sleep latency and 90-minute cycles produces these bedtimes: 12:45 AM (4 cycles, 6h of sleep), 11:15 PM (5 cycles, 7h30m — best fit) and 9:45 PM (6 cycles, 9h). Pick the option that matches how much sleep you need.
Popular sleep guides
- What time should I go to bed? — work backwards from your wake-up time.
- Sleep cycles explained — why the 90-minute rule matters.
- How many hours of sleep do I need? — the 7–9 hour guideline.
- Recommended sleep by age — from newborns to older adults.
Sleep calculator FAQ
Is the sleep calculator medical advice?
No. It produces educational estimates based on average 90-minute sleep cycles. It is not medical advice — talk to a qualified professional about any sleep concerns.
Why are the recommendations 90 minutes apart?
Adults average about 90 minutes per sleep cycle. Waking at the end of a cycle makes waking up feel easier, so the calculator schedules bedtimes and wake times at 4, 5 or 6 full cycles.
What time should I go to bed if I wake up at 7 AM?
With a 7:00 AM wake-up time and 15-minute sleep latency, the calculator suggests 11:15 PM (5 cycles, about 7h30m of sleep) or 9:45 PM (6 cycles, about 9h) as starting points.
What time should I wake up if I go to bed at 11 PM?
With an 11:00 PM bedtime and 15-minute latency, waking at 6:45 AM (5 cycles, about 7h30m) or 8:15 AM (6 cycles, about 9h) usually lands at the end of a full sleep cycle.
What is sleep latency?
Sleep latency is the time it takes you to fall asleep after getting into bed. The calculator assumes 15 minutes by default, and you can adjust it to match your own pattern.
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Understand sleep cycles, latency and how much sleep you really need — in plain language.
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