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Sleep Calculator
Find the best time to go to bed, so you wake up groggy fresh.
Other times
How the sleep calculator works
1. Sleep comes in cycles
Your night is a loop of light, deep and dream (REM) sleep. One loop takes about 90 minutes.
2. Waking mid-cycle hurts
An alarm during deep sleep is why you sometimes feel like a zombie, even after 8 hours.
3. So we time it
We count back whole cycles plus 15 minutes to fall asleep, so a cycle ends right when your alarm rings.
Bedtime chart: what time should I go to bed?
Best bedtimes for common wake-up times. Hours = sleep time (one cycle is 90 minutes), with 15 minutes to fall asleep.
How much sleep do you need?
Recommended sleep per night by age, from the CDC.
| Age | Sleep per night | In cycles |
|---|---|---|
| 6–12 years | 9–12 hours | 6–8 |
| 13–18 years | 8–10 hours | 5–7 |
| 18–60 years | 7 hours or more | 5–6 |
| 61–64 years | 7–9 hours | 5–6 |
| 65+ years | 7–8 hours | 5 |
A planning tool based on average 90-minute sleep cycles, not medical advice. If you're always tired, talk to a doctor.
Questions people ask
How does a sleep calculator work?
Sleep runs in cycles of about 90 minutes. A sleep calculator counts back whole cycles from your wake-up time and adds about 15 minutes to fall asleep, so your alarm goes off at the end of a cycle, in lighter sleep, instead of in the middle of deep sleep.
What time should I go to bed?
Count back 7.5 hours (5 cycles) plus 15 minutes from the time you need to get up. For a 7:00 AM alarm, that means going to bed at 11:15 PM. If you can, 9 hours (6 cycles) is even better: 9:45 PM for a 7:00 AM alarm.
How many sleep cycles do I need?
Most adults do best with 5 or 6 cycles, which is 7.5 to 9 hours. The CDC recommends at least 7 hours a night for adults and 8 to 10 hours for teenagers.
Why do I feel groggy even after enough sleep?
Waking up in the middle of deep sleep causes sleep inertia, that heavy, foggy feeling. Timing your alarm to the end of a cycle can help, and so can daylight and moving around soon after you wake up.
Is every sleep cycle exactly 90 minutes?
No. Cycles usually last 70 to 120 minutes and change through the night, so 90 minutes is an average for planning. If you often wake up just before your alarm, your cycles may be shorter. Try the earlier times.
What if I can't wake up even at the right time?
Heavy sleepers often sleep through their own alarm. A louder or funnier alarm sound helps, and so does someone else making sure you're up. With PingPal, a friend sets the alarm on your phone and you have to send proof you're awake.