Question 1

How does the sleep calculator work?

Accepted Answer

The sleep calculator uses the 90-minute sleep cycle model. Each full sleep cycle takes approximately 90 minutes and includes light sleep, deep sleep and REM sleep stages. Waking up at the end of a cycle — rather than mid-cycle — leaves you feeling more refreshed. Add 15 minutes for average time to fall asleep.

Question 2

How long is a sleep cycle?

Accepted Answer

A complete sleep cycle lasts approximately 90 minutes. Each night, you go through 4 to 6 sleep cycles. The first cycles contain more deep sleep (slow-wave sleep), while later cycles contain more REM sleep, which is critical for memory and mood.

Question 3

How much sleep do I need by age?

Accepted Answer

Recommended sleep by age: Newborns (0-3 months): 14-17 hours. Infants (4-11 months): 12-15 hours. Toddlers (1-2 years): 11-14 hours. Preschoolers (3-5): 10-13 hours. School age (6-13): 9-11 hours. Teenagers (14-17): 8-10 hours. Adults (18-64): 7-9 hours. Older adults (65+): 7-8 hours.

Question 4

What time should I wake up?

Accepted Answer

Enter your bedtime in the sleep calculator above to find the ideal wake-up times based on completing full 90-minute sleep cycles. For 7.5 hours of sleep (5 cycles), go to bed at 10 PM to wake up at 6 AM. Always add 15 minutes for time to fall asleep.

Question 5

What is REM sleep?

Accepted Answer

REM (Rapid Eye Movement) sleep is the stage where most dreaming occurs. It is critical for memory consolidation, emotional processing and creativity. REM sleep occurs mainly in the later cycles of the night, which is why cutting sleep short disproportionately reduces REM sleep.

Question 6

What is sleep debt?

Accepted Answer

Sleep debt is the cumulative difference between the sleep you need and the sleep you actually get. If you need 8 hours but only sleep 6, you accumulate 2 hours of sleep debt per night. Sleep debt cannot be fully repaid in one night and has real effects on cognition, mood and health.

Question 7

Is the 90-minute sleep cycle accurate?

Accepted Answer

The 90-minute cycle is an average. Individual cycles range from 80 to 110 minutes and tend to get longer as the night progresses. The first cycle is typically shorter (70-100 min) and the last can be over 100 minutes. The calculator uses 90 minutes as the standard scientific reference.

Question 8

What time should I go to bed?

Accepted Answer

Enter your desired wake-up time in the bedtime calculator tab above. The tool will calculate the ideal bedtimes based on completing 4, 5 or 6 full sleep cycles (6, 7.5 or 9 hours of sleep), plus 15 minutes to fall asleep.

Question 9

How many hours of sleep do I need?

Accepted Answer

Most adults need 7 to 9 hours per night (4-6 sleep cycles). The exact amount is individual. Signs you are getting enough sleep: you wake up naturally before the alarm, feel alert throughout the day and do not need caffeine to function in the morning.

Question 10

What are the stages of the sleep cycle?

Accepted Answer

A sleep cycle has 4 stages: Stage 1 (NREM) — light sleep, 1-7 minutes. Stage 2 (NREM) — true sleep onset, 10-25 minutes. Stage 3 (NREM) — deep/slow-wave sleep, 20-40 minutes. Stage 4 (REM) — rapid eye movement sleep, 10-60 minutes. These stages repeat every ~90 minutes.

Question 11

Does pulling an all-nighter reset your sleep cycle?

Accepted Answer

Not effectively. Staying up all night disrupts your circadian rhythm but does not cleanly reset it. You may fall asleep earlier the following night due to sleep pressure, but full resynchronization of your internal clock takes several days of consistent sleep timing.

Question 12

What is the best bedtime for kids?

Accepted Answer

Recommended bedtimes by age: 1-2 years: 6:30-7:30 PM. 3-5 years: 7:00-8:00 PM. 6-10 years: 7:30-9:00 PM. 11-13 years: 8:00-9:30 PM. Teenagers: 9:00-10:30 PM. Earlier bedtimes help children complete more slow-wave deep sleep cycles, which are critical for growth hormone release.

Question 13

How accurate is the sleep calculator?

Accepted Answer

The sleep calculator provides scientifically grounded estimates based on average 90-minute sleep cycles and 15 minutes to fall asleep. Individual variation is significant — some people fall asleep in 5 minutes, others take 30. Use the results as guidelines and adjust based on how you feel.

Cycles	Total sleep	Wake-up quality	Recommended for
4 cycles	6 hours	Acceptable	Minimum viable — occasional only
5 cycles	7.5 hours	Good ✓	Most adults — optimal balance
6 cycles	9 hours	Excellent ✓✓	Recovery, teens, athletes
3 cycles	4.5 hours	Poor	Emergency only — not sustainable

Age group	Recommended hours	Sleep cycles
Newborns (0–3 months)	14–17 hours	8–11 cycles
Infants (4–11 months)	12–15 hours	7–9 cycles
Toddlers (1–2 years)	11–14 hours	6–8 cycles
Preschool (3–5 years)	10–13 hours	6–8 cycles
School age (6–13 years)	9–11 hours	5–7 cycles
Teenagers (14–17)	8–10 hours	5–6 cycles
Adults (18–64)	7–9 hours	4–6 cycles
Older adults (65+)	7–8 hours	4–5 cycles

Sleep Calculator

Wake-Up Time Calculator — When Should I Wake Up?

Bedtime Calculator — What Time Should I Go to Sleep?

How Much Sleep Do I Need? — Sleep Calculator by Age

How Long Is a Sleep Cycle?

How Much Sleep Do You Need by Age?

Frequently Asked Questions