Free sleep cycle calculator
Waking up tired isn't about sleep quantity but timing. Sleep works in ~90-minute cycles. Waking up between cycles makes you feel rested, even with fewer hours. This calculator tells you exactly when to go to bed or wake up to optimize your rest.
Includes ~15 min to fall asleep
21:45
6 cycles · 9h of sleep
23:15
5 cycles · 7.5h of sleep
00:45
4 cycles · 6h of sleep
02:15
3 cycles · 4.5h of sleep
03:45
2 cycles · 3h of sleep
05:15
1 cycle · 1.5h of sleep
Ideally aim for 5 or 6 cycles (7h30 or 9h).
How it works
Sleep works in ~90-minute cycles. Each cycle goes through light sleep, deep sleep and REM (dreams). Waking up between cycles, rather than in the middle of one, makes you feel rested and alert.
The science of sleep cycles
- •One cycle lasts about 90 minutes (75-110 min)
- •Deep sleep is concentrated in the first cycles
- •REM sleep increases in the later cycles
- •It takes an average of 10-20 minutes to fall asleep
- •5 to 6 cycles (7h30-9h) is recommended for adults
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Try for freeWhy sleep cycles matter
Each 90-minute cycle goes through 4 stages: falling asleep, light sleep, deep sleep and REM (dreams). Waking up in the middle of a cycle (especially deep sleep) causes sleep inertia — that foggy feeling. Waking up between cycles lets your brain naturally transition to wakefulness.
How to use this calculator
- 1Choose your mode: wake-up time or bedtime
- 2Enter your desired time
- 3The calculator generates optimal times for each cycle count
- 4Aim for 5 or 6 cycles (7h30 or 9h) for optimal sleep
- 5Fall-asleep time (~15 min) is automatically included
Tips for better sleep
- •Go to bed and wake up at the same time, even on weekends
- •Stop screens 1 hour before bed (blue light)
- •Cool bedroom (64-66°F), dark and quiet
- •Avoid caffeine after 2pm
- •Get natural light exposure right after waking up
Frequently asked questions
5 to 6 cycles (7h30-9h) are recommended for adults. 4 cycles (6h) is a functional minimum, but not ideal long-term.
It's an average. Cycles vary from 75 to 110 minutes depending on the individual and time of night. 90 minutes remains the best approximation.
You're probably waking up in the middle of a cycle, during deep sleep. Try going to bed 30 minutes earlier or later to align with a complete cycle.
Short naps (20 min) stay in light sleep. A 90-min nap completes one full cycle. Avoid 45-60 min naps that wake you during deep sleep.