How many sleep cycles do I need?

Most adults need 5–6 complete sleep cycles per night (7.5–9 hours). Each cycle lasts approximately 90 minutes and includes stages of light sleep, deep sleep, and REM sleep.

Why do I wake up tired even after 8 hours?

You may be waking in the middle of a sleep cycle. Waking during deep sleep or REM causes grogginess. Try timing your alarm to the end of a 90-minute cycle.

How long does it take to fall asleep?

The average adult takes 10–20 minutes to fall asleep. This calculator accounts for a 15-minute average. Adjust if you fall asleep faster or slower.

What time should I go to bed?

Use the 'I need to wake up at' mode to calculate optimal bedtimes aligned with complete 90-minute sleep cycles.

Is it better to sleep 6 hours or 7.5 hours?

7.5 hours (5 cycles) is generally better. However, 6 hours ending at a cycle boundary is better than 7 hours that interrupts a cycle mid-way.

Sleep Calculator

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

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Adults need 5–6 complete 90-minute sleep cycles (7.5–9 hours). Waking between cycles reduces grogginess.

Enter your wake-up time below to find your ideal bedtime.

Sleep Cycle Calculator

Wake-up time

Time to fall asleep (minutes)

Average is 10–20 minutes

How to use this tool

1

Choose your mode: bedtime or wake-up time

2

Enter your target time

3

Optionally adjust the time it takes you to fall asleep

Common uses

Finding the ideal bedtime based on your wake-up alarm
Waking up between sleep cycles to feel less groggy
Planning naps that align with natural 90-minute cycles
Adjusting sleep schedules for shift work or jet lag
Understanding how many full sleep cycles you need per night

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