Waking up in the middle of a deep sleep cycle is one reason you can feel groggy even after a long night. Sleep runs in cycles of roughly 90 minutes, and waking at the end of a cycle tends to feel easier. This sleep calculator counts back from the time you need to get up and lists the best times to fall asleep for 3 to 6 full cycles.
Switch to I will go to bed at, or tap I'm going to bed now, to get the best alarm times instead. The calculator adds the time it usually takes to fall asleep (15 minutes by default), and you can change both that and the cycle length to match your own rhythm.
How to use the Sleep Calculator tool
- Choose whether you know your wake-up time or your bedtime.
- Enter the time, or tap I'm going to bed now.
- Adjust how long you usually take to fall asleep, if needed.
- Pick one of the suggested times. Green times give 7.5–9 hours of sleep.
Why use ToolOrca Sleep Calculator
- Bedtimes for a chosen wake-up time
- Alarm times for going to bed now or later
- Adjustable time to fall asleep
- Adjustable cycle length
- Highlights 5–6 cycle options
- Uses your local time format
How sleep cycles work
During the night you move through light sleep, deep sleep and REM (dream) sleep several times. One full round takes about 90 minutes on average, though it varies from about 70 to 120 minutes between people and through the night. Deep sleep is concentrated in the first cycles and REM sleep in the later ones.
Most adults need 7–9 hours of sleep, which is about five or six cycles. Teenagers need 8–10 hours. A short nap of 20 minutes, or a full 90-minute cycle, usually feels better than a 45–60 minute nap that ends in deep sleep.
Frequently asked questions
What time should I go to bed to wake up at 6 am?
For six cycles (9 hours) go to sleep at about 8:45 pm, for five cycles (7.5 hours) at about 10:15 pm, both including 15 minutes to fall asleep.
What time should I go to bed to wake up at 7 am?
About 9:45 pm for six cycles or 11:15 pm for five cycles, including 15 minutes to fall asleep.
Is it better to sleep 6 or 7 hours?
Six hours equals four full cycles and can feel easier to wake from than 7 hours, which ends mid-cycle. But for health, getting enough sleep matters more: most adults need at least 7 hours.
Is a sleep cycle always 90 minutes?
No, 90 minutes is an average. If you regularly wake up just before your alarm, your cycles may be shorter or longer; change the cycle length to fine-tune the times.
Is this medical advice?
No. It is a planning tool only. If you have trouble sleeping or feel tired all the time, speak to a doctor.