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Fitness & Wellbeing

Wake up feeling
rested

Sleep in 90-minute cycles. Enter your wake-up time or bedtime and find the perfect time to sleep — or set your alarm — so you never wake mid-cycle again.

Wake-up time
Time to fall asleep:
14 min
Average is 10–20 minutes. Adjust to match your experience.
🔄
90 min
One sleep cycle (average)
💤
5–6
Ideal cycles per night
⏱️
14 min
Average time to fall asleep
🌙
REM
Vital in later cycles — don't cut short
📱
30 min
Avoid screens before bed
🌡️
18°C
Optimal bedroom temperature
📅 Sleep Log — Last 7 Nights

Why 90-minute cycles?

Each sleep cycle lasts roughly 90 minutes and moves through light sleep, deep sleep, and REM sleep. Waking mid-cycle — especially from deep sleep — causes sleep inertia: that groggy, disoriented feeling. Timing your alarm to the end of a cycle means waking during light sleep, feeling alert naturally.

How many cycles do I need?

Most adults need 5–6 complete cycles (7.5–9 hours). Teenagers need more. Older adults often function on 5. The exact number is individual — use this calculator as a guide and pay attention to how you feel after different amounts. Consistency of schedule matters as much as duration.

What is REM sleep?

REM (Rapid Eye Movement) sleep is the dreaming phase. It's critical for memory consolidation, emotional processing, and creativity. REM sleep is concentrated in the later cycles of the night — cutting sleep short by even one cycle significantly reduces total REM, impacting cognition and mood the next day.

Sleep hygiene basics

Same wake time every day (even weekends) is the single most powerful sleep habit. Avoid caffeine after 2pm (see our Caffeine Calculator). Keep your bedroom cool, dark, and quiet. Avoid screens 30+ minutes before bed. A short wind-down routine signals your brain that sleep is coming.

Frequently Asked Questions
What time should I go to sleep? ▾
It depends on your wake-up time. If you need to wake at 7:00am and take 14 minutes to fall asleep, you should go to bed at 9:46pm (6 cycles), 11:16pm (5 cycles), or 12:46am (4 cycles). Use the calculator above — enter your wake-up time and it will tell you exactly when to go to bed.
Is 6 hours of sleep enough? ▾
For most adults, no. Six hours = 4 sleep cycles, which is below the recommended 5–6. Research consistently shows that chronic 6-hour sleep leads to accumulated cognitive debt, impaired reaction time, mood dysregulation, and increased long-term health risks. A small percentage of people have a genetic variant allowing them to thrive on less — but if you need an alarm to wake up, you're likely not one of them.
Why do I feel worse after more sleep? ▾
This is usually sleep inertia — you woke mid-cycle from deep sleep. More total sleep doesn't mean better sleep if your alarm fires at the wrong point in your cycle. Try using this calculator to time your alarm to the end of a cycle. Irregular sleep schedules also disrupt circadian rhythm, causing grogginess even after long sleep.
Do naps fit into 90-minute cycles? ▾
Yes. A 20-minute "power nap" keeps you in light sleep and avoids grogginess. A 90-minute nap completes one full cycle including REM — great for creativity and memory. The dangerous zone is 30–60 minutes, where you enter deep sleep but don't complete the cycle, causing significant sleep inertia on waking.
Related Tools
😴
Sleep Cycle Calculator
Wake-up times · Sleep cycle science
→
😴
Sleep Debt Tracker
Accumulated deficit · Recovery plan
→
🌤️
Mood & Sleep Tracker
Sleep + mood correlation · Daily log
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🔔
Meditation Timer
Bells · Intervals · Streak log
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How to Use the Sleep Calculator

Find the best times to go to sleep or wake up based on 90-minute sleep cycles.

01
Choose your calculation direction
'I need to wake up at...' — enter your wake time and see the best bedtimes. 'I want to go to sleep at...' — enter your bedtime and see the best wake times.
02
Allow for sleep onset time
The calculator adds 15 minutes to account for the time it takes to fall asleep. If you fall asleep quickly, subtract 5 minutes; if it takes longer, add more.
03
Pick a full cycle count
The results show bedtimes for 5 and 6 complete cycles (7.5 and 9 hours). Waking mid-cycle (e.g. after 7 hours) often feels worse than waking after 6 or 7.5 hours.
04
Use it to time naps
A 90-minute nap completes one full cycle and includes deep sleep. A 20-minute power nap stays in light sleep and avoids grogginess. Both have value; the 20-minute nap is safer if you need to function immediately after.
💡
💡 The reason an alarm often feels brutal is that it interrupts deep sleep. Sleeping in 90-minute increments means you're more likely to wake naturally at a light sleep stage, feeling more rested even on the same total hours.