Calculate Your Optimal Bedtime
There's no single perfect bedtime. But there is one that fits your body. It depends on your individual sleep need, your chronotype, and your daily routine.
Why there's no universal bedtime
Most adults need between 7 and 9 hours of sleep per night.[5] But that's just the average. Some people do fine on 6 hours, others need 9.5. What matters isn't just how long you sleep, but when.
Sleep researcher Till Roenneberg showed in 2003 that preferred sleep timing is partly genetic.[1] Early types (larks) naturally sleep from around 10 PM to 6 AM, late types (owls) from around 1 AM to 9 AM. Neither type is better or healthier. The problem only arises when your schedule doesn't match your biological rhythm.
Understanding sleep cycles
Sleep occurs in cycles of roughly 90 minutes.[4] Each cycle progresses through light sleep, deep sleep, and REM sleep. You go through 4 to 6 of these cycles per night, with brief wake periods between them that you usually don't remember.
Waking between cycles generally feels better than being pulled out of deep sleep. That's the idea behind many online sleep calculators.
But here's the catch: the 90-minute rule is an average. Actual cycle length varies between 75 and 110 minutes, and it changes over the course of the night.[4] Rigid calculators based on exact 90-minute blocks are therefore inaccurate.
Your chronotype sets the rhythm
Your chronotype describes your internal clock. It's measured via MSFsc (Mid-Sleep on Free Days, sleep-corrected), a metric from chronobiology.[1] In simple terms: when would you sleep if you never had to set an alarm?
When your work or school schedule doesn't match your chronotype, social jetlag occurs: the chronic mismatch between your biological and social clock.[2] It's like flying to a different time zone every weekday. The consequences: higher sleep debt, poorer recovery, and measurably lower performance.
Learn more in our chronotype article.
Sleep need is individual
Kitamura et al. (2016) developed a method to derive individual sleep need from extended sleep periods.[3] The result: the average is about 7.5 hours, but the spread is wide. Anywhere between 6 and 9 hours is normal.
A common belief is that sleep need decreases with age. Ohayon et al. (2004) paint a more nuanced picture: need stays relatively stable, but the ability to maintain consolidated sleep declines.[5] Older adults don't need less sleep, they just get less.
What the app does differently
Most bedtime calculators use a fixed formula: wake time minus sleep duration, maybe adjusted for 90-minute cycles. That's not enough.
Circadian calculates your optimal bedtime from real sleep data: actual sleep and wake times over several weeks, your chronotype (detected automatically), your current sleep debt, and your energy trajectory. The bedtime recommendation adapts daily, because your body changes daily.
Calculator: Your Optimal Bedtime
Note: This calculator assumes a sleep onset latency (SOL) of 15 minutes. Chronotype shifts the recommendation by 30 minutes. For a precise calculation, you need real sleep data over several weeks.
Sleep cycles last between 75 and 110 minutes. The displayed cycle count is a rough estimate.
Plan better. Sleep better.
Circadian Energy doesn't calculate your bedtime from a rigid formula. It uses your real sleep data and your personal energy curve.
- Recommends bedtime and wake times based on your chronotype
- Adapts the recommendation daily to your current sleep debt
- Detects your chronotype automatically from your sleep patterns
- Calculates your energy curve daily from real Apple Health sleep data
- No subscription, no account, 100% on your device
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References
- Roenneberg T, Wirz-Justice A, Merrow M (2003). Life between clocks: daily temporal patterns of human chronotypes. Journal of Biological Rhythms, 18(1), 80-90.
- Roenneberg T, Allebrandt KV, Merrow M, Vetter C (2012). Social jetlag and obesity. Current Biology, 22(10), 939-943.
- Kitamura S, Katayose Y, Nakazaki K, et al. (2016). Estimating individual optimal sleep duration and potential sleep debt. Scientific Reports, 6, 35812.
- Carskadon MA, Dement WC (2011). Normal Human Sleep: An Overview. In: Kryger MH, Roth T, Dement WC (Eds.), Principles and Practice of Sleep Medicine (5th ed.), Elsevier.
- Ohayon MM, Carskadon MA, Guilleminault C, Vitiello MV (2004). Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals. Sleep, 27(7), 1255-1273.