Sleep Calculator
Enter when you need to wake up, or when you plan to go to bed, and get the times that land at the end of a full sleep cycle rather than in the middle of deep sleep, with the amount of sleep recommended for your age.
Adult (26-64): 7–9 hours recommended.
10-20 minutes is normal. Under 5 suggests you are sleep deprived; over 30 regularly is worth a look.
6 cycles · 9 h
9:15 PM
in your recommended range
5 cycles · 7 h 30 min
10:45 PM
in your recommended range
4 cycles · 6 h
12:15 AM
under your recommended range
3 cycles · 4 h 30 min
1:45 AM
under your recommended range
Lights out at one of these and you should wake at the end of a 90-minute cycle, in light sleep, at 6:30 AM.
Bedtime chart by wake-up time
Lights-out times that put your alarm at the end of a 90-minute cycle, with 15 minutes to fall asleep. Five or six cycles is the adult range.
| Wake up | 6 cycles · 9 h | 5 cycles · 7.5 h | 4 cycles · 6 h | 3 cycles · 4.5 h |
|---|---|---|---|---|
| 5:00 AM | 7:45 PM | 9:15 PM | 10:45 PM | 12:15 AM |
| 5:30 AM | 8:15 PM | 9:45 PM | 11:15 PM | 12:45 AM |
| 6:00 AM | 8:45 PM | 10:15 PM | 11:45 PM | 1:15 AM |
| 6:30 AM | 9:15 PM | 10:45 PM | 12:15 AM | 1:45 AM |
| 7:00 AM | 9:45 PM | 11:15 PM | 12:45 AM | 2:15 AM |
| 7:30 AM | 10:15 PM | 11:45 PM | 1:15 AM | 2:45 AM |
| 8:00 AM | 10:45 PM | 12:15 AM | 1:45 AM | 3:15 AM |
| 9:00 AM | 11:45 PM | 1:15 AM | 2:45 AM | 4:15 AM |
How much sleep you need, by age
National Sleep Foundation consensus ranges (Hirshkowitz et al., 2015). "May be appropriate" is the wider band some healthy people fall in; outside it is a reason to look at what is going on.
| Age | Recommended | May be appropriate | In 90-min cycles |
|---|---|---|---|
| Newborn (0-3 mo) | 14–17 h | 11–19 h | 9–11 |
| Infant (4-11 mo) | 12–15 h | 10–18 h | 8–10 |
| Toddler (1-2) | 11–14 h | 9–16 h | 7–9 |
| Preschool (3-5) | 10–13 h | 8–14 h | 7–9 |
| School age (6-13) | 9–11 h | 7–12 h | 6–7 |
| Teen (14-17) | 8–10 h | 7–11 h | 5–7 |
| Young adult (18-25) | 7–9 h | 6–11 h | 5–6 |
| Adult (26-64) | 7–9 h | 6–10 h | 5–6 |
| Older adult (65+) | 7–8 h | 5–9 h | 5–5 |
What a night looks like
Each cycle runs light sleep (N1, N2) into deep slow-wave sleep (N3) and ends in REM. The mix shifts across the night: the first two cycles are heavy on deep sleep, the last two on REM. Cutting a night short from 7.5 to 6 hours does not remove 20% of everything; it removes most of the last REM period, which is why short nights hit mood and memory before they hit the body.
| Cycle | After lights out | Character |
|---|---|---|
| 1 | 15 min–1 h 45 min | Mostly deep sleep; a short REM period. |
| 2 | 1 h 45 min–3 h 15 min | Still deep-sleep heavy; REM lengthens. |
| 3 | 3 h 15 min–4 h 45 min | Balanced; the halfway point. |
| 4 | 4 h 45 min–6 h 15 min | Light and REM dominate; deep sleep fading. |
| 5 | 6 h 15 min–7 h 45 min | Long REM period; easy to wake from -- the natural end. |
Making the number stick
- Fix the wake time, not the bedtime. Same alarm seven days a week anchors the body clock; bedtime then takes care of itself within a couple of weeks.
- Lights out means lights out. The 14 minutes assume darkness and no screen. Scrolling in bed adds 20-40 minutes of latency and shifts every time in the table.
- Give a new schedule two weeks. Cycle boundaries drift; consistency trains the last cycle to end near the alarm.
- If you regularly can't fall asleep in 30 minutes or wake for long stretches, that is insomnia territory and a calculator will not fix it. Cognitive behavioural therapy for insomnia (CBT-I) has better evidence than any pill.
Frequently Asked Questions
What time should I go to bed if I wake up at 6:30?
Lights out at 10:45 PM for five cycles (7.5 hours asleep) or 9:15 PM for six (9 hours), allowing 14 minutes to fall asleep. Four cycles (6 hours) means 12:15 AM, which is under the adult recommendation and best kept for the odd night.
How much sleep do I actually need?
Adults 18 to 64: 7 to 9 hours; over 65: 7 to 8; teenagers 8 to 10; school-age children 9 to 11. Those are the National Sleep Foundation's recommended ranges. Inside the range, the right amount is the one where you wake without an alarm most days and don't crash at 3 p.m. Genuine short sleepers who thrive on under six hours are rare, well under 1% of adults, and most people who think they are one are simply sleep deprived.
Why 90 minutes, and why 14 minutes to fall asleep?
A full sleep cycle -- light, deep, then REM -- averages about 90 minutes in adults, with a real range of 70 to 120, and cycles lengthen through the night. Waking at the end of a cycle, in light sleep, feels far better than an alarm in deep sleep 45 minutes in. Healthy adults take 10 to 20 minutes to fall asleep; 14 is the midpoint. Adjust the slider if you know you drop off faster or slower.
Is it better to sleep 6 hours or 7.5?
7.5, almost always. The 'better to wake at the end of a cycle' idea is about which alarm to set given the sleep you can get, not a reason to cut sleep to hit a cycle boundary. If the choice is 6 hours ending on a boundary or 7 hours ending mid-cycle, take the 7 and set the alarm 10 minutes later.
Does it matter what time I go to bed, or only how long I sleep?
Both. Deep sleep is front-loaded in the first cycles and REM is back-loaded, and both track your body clock, not just elapsed time. Sleeping 7 hours from 11 p.m. and 7 hours from 3 a.m. are not equivalent: the late night gets less deep sleep and is cut short of REM by daylight. A consistent bedtime and, more importantly, a consistent wake time are worth more than any calculator.
These calculators use published sleep-science guidelines and are for general guidance. They are estimates, not medical advice: persistent insomnia, loud snoring or gasping in sleep, or daytime sleepiness that affects driving are reasons to see a doctor, not to adjust a bedtime.