Sleep Calculator

Find your perfect bedtime or wake-up time with 90-minute sleep cycles. Use the scroll-wheel picker or quick presets, then set a one-tap countdown reminder.

Sleep Calculator

Calculate the optimal time to sleep or wake up based on 90-minute sleep cycles.

This calculator is based on sleep cycle science:

• Each sleep cycle lasts approximately 90 minutes
• 5–6 complete cycles (7.5–9 hours) is recommended for adults
• Allow ~15 minutes to fall asleep after lying down

I want to wake up at

Suggested bedtimes

9:45 PMRecommended

6 cycles • 9h 0m sleep

Set ReminderSleep in 15h 47m

11:15 PMRecommended

5 cycles • 7h 30m sleep

Set ReminderSleep in 17h 17m

12:45 AM

4 cycles • 6h 0m sleep

Set ReminderSleep in 18h 47m

2:15 AM

3 cycles • 4h 30m sleep

Set ReminderSleep in 20h 17m

3:45 AM

2 cycles • 3h 0m sleep

Set ReminderSleep in 21h 47m

5:15 AM

1 cycles • 1h 30m sleep

Set ReminderSleep in 23h 17m

Sleep Tips

• Maintain a consistent sleep schedule, even on weekends
• Keep your bedroom dark, quiet, and cool (around 18–20 °C)
• Avoid caffeine and screens at least 1 hour before bed
• A relaxing pre-sleep routine signals your body it's time to rest

How It Works

Sleep Cycles

Sleep occurs in repeating 90-minute cycles of light, deep, and REM sleep. Waking at the end of a cycle leaves you feeling most refreshed.

Optimal Duration

5–6 complete cycles (7.5–9 hours) is the recommended sleep duration for most adults to support health and performance.

Fall-Asleep Time

On average it takes about 15 minutes to fall asleep after getting into bed, which is factored into every calculation.

Features

Two Calculation Modes

Calculate the ideal bedtime from your desired wake-up time, or find the best wake-up time from your planned bedtime.

Quick Presets

Tap a chip to instantly load a common time — bedtime mode: Now, +10 min, +30 min, +1 h; wake-up mode: popular alarm times from 5:30–9:00 AM.

Countdown Reminder

Click 'Set Reminder' on any result to instantly launch a countdown timer that alerts you when it's time to sleep or wake up.

Works Everywhere

Fully responsive design works seamlessly on phones, tablets, and desktops.

FAQ

Frequently Asked Questions

Find out all the essential details about our platform and how it can serve your needs.

How long is a sleep cycle?

A complete sleep cycle lasts approximately 90 minutes and includes light sleep, deep sleep (slow-wave), and REM stages.

How many sleep cycles do I need?

Most adults need 5–6 complete cycles (7.5–9 hours). Fewer than 4 cycles is generally considered insufficient rest.

Why is there a 15-minute offset?

The average person takes around 15 minutes to fall asleep after lying down. This latency is added to all calculations so the results reflect real sleep, not just time in bed.

How do I use the countdown reminder?

Click 'Set Reminder' next to any suggested time. A countdown timer will open and alert you when it's time to sleep or wake up.

What if I can't fall asleep at the recommended time?

The times are guidelines, not strict rules. Try to aim for the closest recommended window. Even completing 4 cycles is far better than waking mid-cycle.

What are the quick preset buttons?

Quick presets let you set the time in one tap without scrolling the wheel. In 'Bedtime → Wake-up' mode, choose Now, +10 min, +20 min, +30 min, +1 h, or +1 h 30 m to set how soon you plan to sleep. In 'Wake-up → Bedtime' mode, tap a common alarm time (5:30–9:00 AM) to instantly fill the picker.

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