Find the best time to wake up or go to sleep based on 90-minute sleep cycles.
Wake up feeling refreshed — not groggy.
100% FreeNo Sign-upsBased on Sleep ScienceInstant Results
Choose a Calculation
⏰
I want to wake up at...
When should I go to sleep?
🌙
I want to sleep at...
When should I wake up?
Recommended Sleep Times
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How Sleep Cycles Work
Each sleep cycle lasts approximately 90 minutes and moves through light sleep, deep sleep, and REM (dream) sleep. Waking up at the end of a cycle — rather than in the middle — is what makes the difference between feeling alert and feeling groggy.
Light
Deep
REM
Light
One 90-minute sleep cycle
Cycles
Total Sleep
Quality
3 cycles
4.5 hrs
⚠️ Minimum
4 cycles
6 hrs
Fair
5 cycles
7.5 hrs
✓ Recommended
6 cycles
9 hrs
⭐ Optimal
Tips for Better Sleep
📱
No screens 1hr before bedBlue light suppresses melatonin production and delays sleep onset
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Cool room (16–18°C)Your body temperature drops to initiate sleep — a cool room helps
☕
No caffeine after 2pmCaffeine has a 6-hour half-life — a 3pm coffee still affects you at 9pm
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Consistent sleep scheduleGoing to bed and waking at the same time each day regulates your body clock
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Make your room darkEven small amounts of light can reduce melatonin and disrupt deep sleep
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Wind-down routineA consistent pre-sleep routine signals your brain that sleep is coming
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Frequently Asked Questions
How does the sleep calculator work? +
The calculator works backwards or forwards from your chosen time in 90-minute increments — the length of one complete sleep cycle. Waking up at the end of a cycle (rather than mid-cycle) dramatically reduces morning grogginess. It also accounts for the average time it takes to fall asleep.
How many sleep cycles do I need? +
Most adults need 5–6 complete sleep cycles per night (7.5–9 hours). Fewer than 4 cycles (under 6 hours) consistently leads to sleep deprivation. The NHS recommends 7–9 hours for adults.
What is REM sleep? +
REM (Rapid Eye Movement) sleep is the dream stage of sleep and is critical for memory consolidation, emotional processing, and creativity. REM periods get longer in each successive cycle, which is why a full night's sleep is so important — early cycles have less REM than later ones.
Why do I feel worse after more sleep sometimes? +
This is called sleep inertia — the groggy feeling from waking up mid-cycle. If you sleep for a non-multiple of 90 minutes (e.g. 8 hours), you wake up partway through a cycle. The sleep calculator helps you time your wake-up to the end of a cycle to avoid this.