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Sleep Calculator
Find a bedtime or wake-up time that lets you finish a full sleep cycle instead of being pulled out of the middle of one. Enter when you need to wake up — or when you are going to bed — and get times for three to six 90-minute cycles, allowing about 15 minutes to fall asleep.
- 6 cycles · 9 h of sleep
- 9:45 PM
- 4 cycles · 6 h of sleep
- 12:45 AM
- 3 cycles · 4 h 30 min of sleep
- 2:15 AM
Saved setups
Save a set of inputs you reuse — your usual rate, your loan, your room sizes — and load it back in one tap.
Your recent calculations
Results you calculate here are kept on this device so you can come back to them.
Formula
How to use it
- Choose whether you want a bedtime or a wake-up time.
- Enter the time you need to wake up, or the time you plan to get into bed.
- Adjust the time it takes you to fall asleep if 15 minutes does not fit you.
- Pick the option that gives you enough sleep — five or six cycles for most adults.
Worked examples
Waking at 7:00 am — bedtimes, allowing 15 minutes to fall asleep
- 6 cycles · 9 h of sleep
- 9:45 PM
- 5 cycles · 7 h 30 min of sleep
- 11:15 PM
- 4 cycles · 6 h of sleep
- 12:45 AM
- 3 cycles · 4 h 30 min of sleep
- 2:15 AM
Going to bed at 11:00 pm — wake-up times
- 3 cycles · 4 h 30 min of sleep
- 3:45 AM
- 4 cycles · 6 h of sleep
- 5:15 AM
- 5 cycles · 7 h 30 min of sleep
- 6:45 AM
- 6 cycles · 9 h of sleep
- 8:15 AM
Why 90 minutes
Sleep runs in cycles of light sleep, deep sleep and REM sleep that average about 90 minutes, though anything from roughly 70 to 120 minutes is normal and the length changes through the night. Waking at the end of a cycle, in light sleep, tends to feel easier than being woken from deep sleep.
Because your own cycles will not be exactly 90 minutes, treat the times as a starting point and shift them by 10 or 15 minutes to see what suits you. Getting enough total sleep matters more than hitting the cycle boundary.
How much sleep adults need
US sleep and public-health bodies recommend at least 7 hours a night for adults, with 7 to 9 hours the usual range. The four- and three-cycle options (6 hours and 4.5 hours) are shown for the occasional short night, not as a routine.
This is an estimate for general information, not medical advice. Talk to a doctor or other qualified clinician before making health decisions based on it.
Questions people ask
What time should I go to bed to wake up at 7 am?
11:15 pm for five cycles (7.5 hours of sleep) or 9:45 pm for six cycles (9 hours), allowing 15 minutes to fall asleep.
If I go to bed at 11 pm, when should I wake up?
6:45 am after five cycles or 8:15 am after six, assuming you fall asleep at about 11:15 pm.
Is 6 hours of sleep enough?
For most adults, not as a habit. Six hours is four cycles, and the recommended amount is at least seven hours a night.