Can I use custom cycle lengths (e.g., 75 minutes)?

Yes. The 'Shift-Work / Custom' mode is designed for this purpose. If you've tracked your sleep and found your cycles are shorter or longer than the average 90 minutes, you can input your specific cycle length for more personalized calculations.

How do I plan sleep around shift work?

Shift workers can use the 'Bedtime Planner' or 'Wake-time Planner' modes to schedule sleep windows that fit their changing schedules. The key is to calculate backwards or forwards in full sleep cycles from when you need to wake up or go to sleep, helping to maximize the quality of the sleep you can get.

Why does waking at the end of a sleep cycle feel easier?

At the end of a sleep cycle, your brain is in a lighter stage of sleep, closer to wakefulness. Being woken during this phase is less jarring than being pulled from deep slow-wave sleep. This can significantly reduce morning grogginess, also known as sleep inertia.

Sleep Cycle Calculator — Bedtime & Wake-time Planner Using 90-minute Sleep Cycles

Sleep Cycle Calculator

Align Bedtimes & Wake Times with Natural Sleep Cycles

I want to wake up at:

Time to fall asleep (minutes):

Sleep cycle length (minutes):

Pre-sleep wind-down (minutes):

I will go to bed at:

Keyboard shortcuts: Enter = Calculate, Esc = Reset.

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Please check your inputs and try again.

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What Are Sleep Cycles and Why 90 Minutes?

When you sleep, your brain doesn't just switch off. Instead, it cycles through several distinct stages, including light sleep, deep sleep, and Rapid Eye Movement (REM) sleep. A full journey through these stages is called a sleep cycle. For most adults, one complete cycle lasts about 90 minutes on average.

The magic of a sleep cycle calculator lies in timing your awakening. If your alarm clock jolts you out of a deep sleep stage, you're likely to feel groggy and disoriented—a feeling known as sleep inertia. By planning to wake up at the end of a cycle, when your body is naturally in a lighter stage of sleep, you can feel significantly more refreshed and ready to start your day.

How to Use the Sleep Cycle Calculator

This tool is designed to be simple and flexible. Here's how to get the most out of it:

Select Your Mode: Choose "Wake-up Time" if you know when you need to be up, or "Bedtime" if you know when you plan to sleep.
Enter Your Time: Input your desired wake-up or bedtime.
Adjust Your Settings:
- Time to fall asleep: Be realistic. Most people don't fall asleep the moment their head hits the pillow. The default is 15 minutes.
- Sleep cycle length: 90 minutes is a good average, but if you've tracked your sleep and know your cycle is different, you can adjust it (between 60-120 minutes).
Calculate: The tool will provide several optimal times. The main recommendation is based on getting 5-6 cycles (7.5-9 hours of sleep), but it also shows alternatives so you can choose what works best for your schedule.

Nap Science & Avoiding Sleep Inertia

Naps can be a powerful tool for boosting alertness and performance, but timing is everything. The wrong nap length can leave you feeling worse than before.

The Power Nap (10-20 minutes): This short nap improves alertness and energy without pushing you into deep sleep. It's ideal for a quick midday boost with minimal risk of grogginess.
The Full-Cycle Nap (approx. 90 minutes): This allows you to complete one full sleep cycle, including restorative deep sleep and REM sleep. It can enhance creativity and memory consolidation, but you must complete the full cycle to avoid waking up during deep sleep.
The Avoid Zone (30-60 minutes): Napping for this duration often means waking up during your deepest stage of sleep, which can cause significant sleep inertia that can last for over an hour.

Frequently Asked Questions

What is a sleep cycle and why are they ~90 minutes?

A sleep cycle is a progression through different stages of sleep, from light sleep to deep sleep and then REM (Rapid Eye Movement) sleep. One full cycle takes approximately 90 minutes on average. Waking up at the end of a cycle, rather than in the middle of a deep sleep stage, can help you feel more refreshed and less groggy.

How many sleep cycles should I aim for per night?

Most adults need 7-9 hours of sleep per night, which corresponds to about 5-6 full sleep cycles. However, individual needs vary. Four cycles (6 hours) may be sufficient for some, while others might need six cycles (9 hours) to feel fully rested.

How do I calculate bedtime for a 7:00 AM wake-up?

Using this calculator, set your wake-up time to 7:00 AM. For 5 sleep cycles (7.5 hours), a good bedtime would be around 11:15 PM, accounting for about 15 minutes to fall asleep. For 6 cycles (9 hours), you would aim for a 9:45 PM bedtime. The tool automatically does this math for you.

Are sleep cycles the same for everyone?

No. While 90 minutes is a common average, an individual's sleep cycle can range from about 70 to 120 minutes. Advanced modes in this calculator allow you to adjust the cycle length to better match your personal sleep patterns if you know them.

What is a power nap vs a full-cycle nap?

A power nap is a short sleep of 10-20 minutes that ends before you enter deep sleep. It's great for a quick energy boost without grogginess (sleep inertia). A full-cycle nap is around 90 minutes, allowing you to complete one full sleep cycle, which can improve memory and creativity.

Disclaimer

Health & Safety Note: This tool provides planning guidance only and is not a substitute for medical advice. For persistent sleep problems, chronic insomnia, or other sleep disorders, please consult a qualified healthcare professional. Consistent, quality sleep is crucial for health, and this tool should be used to support, not replace, healthy sleep habits.

Privacy Note: All calculations are performed on your device. No data is sent to or stored on our servers. Any schedules you choose to save are stored only in your browser's local storage.

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Sleep Cycle Calculator