AIAZHHow To Use
- Choose your mode: find ideal bedtimes based on wake time, or find ideal wake times based on bedtime.
- Enter the time you need to wake up (or plan to go to bed).
- Adjust the minutes it typically takes you to fall asleep (default 15).
- Click "Calculate" to see recommended bedtimes or wake times based on complete sleep cycles.
- Choose a time that fits your schedule and aim for 5-6 complete cycles (7.5-9 hours).
Frequently Asked Questions
What are sleep cycles?
Sleep cycles are 90-minute periods during which your brain progresses through light sleep, deep sleep, and REM sleep. Waking up at the end of a cycle (rather than in the middle) leaves you feeling more rested.
How many sleep cycles do I need?
Most adults need 5-6 complete sleep cycles per night, which equals 7.5-9 hours of sleep. Some people function well on 4 cycles (6 hours), while others need 6 cycles (9 hours).
Why do I feel tired when my alarm goes off?
You are likely waking up in the middle of a sleep cycle. The sleep calculator helps you set a wake time that aligns with the end of a cycle, so you wake up during light sleep feeling more refreshed.
Does the sleep calculator work for shift workers?
Yes. The sleep calculator works for any sleep schedule, including night shifts and rotating shifts. Just enter your desired wake time or bedtime, regardless of whether it is day or night.
Is my sleep data stored or shared?
No. All calculations are performed locally in your browser. Your sleep schedule data never leaves your device.
What if I cannot fall asleep immediately?
The calculator includes a "minutes to fall asleep" adjustment. If you typically take 15 minutes to fall asleep, enter that value. The calculator accounts for this when suggesting bedtimes so you still complete full cycles.
Sleep Cycle Optimization
Based on 90-minute sleep cycles. Waking at the end of a cycle leaves you feeling more refreshed than waking mid-cycle.
Bedtime & Wake Time Modes
Two modes: enter your wake time to find ideal bedtimes, or enter your bedtime to find ideal wake times. Works for any schedule.
100% Private & Secure
Your sleep data never leaves your device. All calculations happen locally in your browser with JavaScript.
Free & No Signup
No account required, no email needed. Use the sleep calculator unlimited times for free.
Optimize Your Sleep with Cycle-Based Scheduling
Our free sleep calculator helps you wake up feeling refreshed by aligning your sleep schedule with natural 90-minute sleep cycles. Whether you need to find the best bedtime for a specific wake time or the best wake time for your bedtime, the calculator does the math for you.
The Science of Sleep Cycles and Circadian Rhythms
Sleep is not a single continuous state — it alternates between light sleep, deep sleep, and REM sleep in approximately 90-minute cycles. Your circadian rhythm regulates when you feel sleepy and alert. By aligning your sleep schedule with both cycles and rhythm, you can improve sleep quality significantly.
How to Improve Your Sleep Quality
Beyond timing, improve sleep quality by: keeping a consistent schedule (even on weekends), avoiding screens 1 hour before bed, keeping your bedroom cool (18-20°C), reducing caffeine after 2 PM, and limiting alcohol before bed. These habits complement the sleep calculator for best results.
How Much Sleep Do Adults Really Need?
Most adults need 7-9 hours per night. Sleep needs vary individually — some people feel great on 7 hours while others need 9. Use the sleep calculator to try different bedtimes and wake times, and pay attention to how you feel. The right amount is what leaves you feeling rested without an alarm.