Sleep Calculator
Best bedtime or wake-up time using 90-minute sleep cycles, plus sleep needs by age
| Age group | Age | Hours / day |
|---|---|---|
| Newborns | 0–3 months | 14–17 |
| Infants | 4–11 months | 12–15 |
| Toddlers | 1–2 years | 11–14 |
| Preschool | 3–5 years | 10–13 |
| School age | 6–13 years | 9–11 |
| Teenagers | 14–17 years | 8–10 |
| Young adults | 18–25 years | 7–9 |
| Adults | 26–64 years | 7–9 |
| Older adults | 65+ years | 7–8 |
Runs entirely in your browser. Nothing you type or upload is sent to us or stored.
For general information only, not medical advice. Talk to a doctor or a qualified professional about your health. Terms of use
How to Use
- Choose I want to wake up at to find bedtimes, I'm going to bed at to find wake-up times, or Sleeping now to use the current time.
- Pick the time with the time picker (for example 6:30 AM).
- Adjust Time to fall asleep (15 minutes by default) and One sleep cycle (90 minutes by default) if you know yours are different.
- The main answer shows the 5-cycle option (7½ hours of sleep at 90-minute cycles); the list also gives 6, 4 and 3 cycles, with 5 and 6 marked as recommended for adults.
- Tap copy times to paste the list into a note or message, or reset to start again.
- Check the Recommended sleep by age table to see how many hours children, teenagers and adults need.
Wake up between sleep cycles, not in the middle of one
Sleep is not one long, even stretch. Through the night you pass through repeated cycles of light sleep, deep sleep and REM (dreaming) sleep, each lasting roughly 90 minutes on average. Waking from deep sleep is what leaves you groggy and heavy-headed; waking near the end of a cycle, when sleep is lighter, usually feels easier. This calculator counts back (or forward) in whole cycles from the time you need to wake, so your alarm rings at a natural break.
How the times are calculated
Wake-up time = bedtime + time to fall asleep + (cycles × cycle length)
With the defaults of 90-minute cycles and 15 minutes to fall asleep, 6 cycles is 9 hours of sleep, 5 cycles is 7½ hours, 4 cycles is 6 hours and 3 cycles is 4½ hours. Five or six cycles fit the 7–9 hours most adults need, so those are marked as recommended.
Worked example
A student has to wake at 6:30 AM for school or coaching. Counting back:
- 6 cycles: 6:30 AM − 9 h − 15 min = 9:15 PM
- 5 cycles: 6:30 AM − 7 h 30 min − 15 min = 10:45 PM
- 4 cycles: 12:15 AM (only 6 hours: fine now and then, not every night)
For a teenager, who needs 8–10 hours, 9:15 PM is the better choice. Going to bed at 11:00 PM instead gives wake-up times of 5:15 AM (4 cycles), 6:45 AM (5 cycles) or 8:15 AM (6 cycles).
Sleep needs by age (AASM guidance)
The table in the tool lists the National Sleep Foundation's 2015 recommendations. The American Academy of Sleep Medicine (AASM) gives very similar ranges:
| Age | Hours per 24 hours (AASM) |
|---|---|
| 4–12 months | 12–16, including naps |
| 1–2 years | 11–14, including naps |
| 3–5 years | 10–13, including naps |
| 6–12 years | 9–12 |
| 13–18 years | 8–10 |
| Adults 18–60 years | 7 or more |
Sources: Paruthi et al., AASM consensus statement for children, Journal of Clinical Sleep Medicine, 2016; Watson et al., AASM and Sleep Research Society recommendation for adults, 2015; Hirshkowitz et al., National Sleep Foundation, Sleep Health, 2015.
Limits of the 90-minute rule
- Cycle length varies from person to person and through the night (roughly 70–120 minutes), so treat the times as a guide. If you often wake just before the alarm, your cycles may be shorter: try 80 or 85 minutes.
- Total sleep matters more than hitting a cycle exactly. Six hours timed perfectly is still too little for most people night after night.
- A regular schedule (the same bedtime and wake time, even on Sundays) helps more than any calculator.
- Loud snoring with pauses in breathing, or daytime sleepiness despite enough hours, can be signs of sleep apnoea or another sleep disorder; see a doctor.
Tips for falling asleep on time
- Put the phone away 30–60 minutes before bed; bright screens and endless reels push sleep later.
- Avoid tea, coffee and cola in the evening, and keep heavy dinners at least two to three hours before bed.
- Keep the room dark, quiet and cool; a fan or white noise can mask traffic sounds.
- Get daylight in the morning. It helps set your body clock for the next night.