Sleep Calculator (Bedtime & Wake-Up Time)
By Santaji GadepatilinUpdated October 27, 2026
Sleep runs in cycles of about 90 minutes. Waking at the end of a cycle, rather than in the middle, helps you feel more refreshed.
How to use the sleep calculator
Enter your bedtime, choose the number of sleep cycles and how long you usually take to fall asleep. The best wake-up time is calculated. To plan a bedtime, press × on Bedtime and type the time your alarm must ring.
Why cycles?
Sleep moves through light, deep and REM stages in cycles of roughly 90 minutes. Waking at the end of a cycle — rather than in deep sleep — usually feels easier.
Example
Bed at 22:45, 15 minutes to fall asleep, 5 cycles: wake at 06:30 (7.5 hours of sleep).
Bedtimes for common wake-up times
Including 15 minutes to fall asleep:
| Wake-up time | 6 cycles (9 h) | 5 cycles (7.5 h) | 4 cycles (6 h) |
|---|---|---|---|
| 5:30 | 20:15 | 21:45 | 23:15 |
| 6:00 | 20:45 | 22:15 | 23:45 |
| 6:30 | 21:15 | 22:45 | 0:15 |
| 7:00 | 21:45 | 23:15 | 0:45 |
| 7:30 | 22:15 | 23:45 | 1:15 |
| 8:00 | 22:45 | 0:15 | 1:45 |
How much sleep do you need?
| Age group | Recommended hours per night |
|---|---|
| Teenagers (13–18) | 8–10 |
| Adults (18–64) | 7–9 |
| Older adults (65+) | 7–8 |
These ranges come from the US National Sleep Foundation and the American Academy of Sleep Medicine. Five cycles (7.5 hours) suits many adults.
Cycles are an average
Sleep cycles last about 80–110 minutes and change through the night. Treat the 90-minute cycle as a guide. If you often wake before the alarm feeling refreshed, your body has found its own rhythm.
When to seek help
Talk to a doctor if you snore loudly, stop breathing during sleep, feel very sleepy in the day despite enough hours, or have trouble sleeping most nights for weeks.
Better sleep habits
- Keep a regular schedule, even at weekends.
- Avoid caffeine late in the day.
- Keep the bedroom dark, quiet and cool.
- Put screens away 30–60 minutes before bed.
Frequently asked questions
How long is a sleep cycle?
About 90 minutes on average, though it varies between 70 and 120 minutes from person to person and through the night.
How much sleep do adults need?
Health organisations recommend 7 or more hours for adults — usually 5 or 6 cycles.
How do I find when to go to bed?
Press × on Bedtime and enter the time you need to wake up.
What time should I go to bed to wake up at 6 AM?
Around 10:15 PM for five 90-minute cycles, or 8:45 PM for six, allowing 15 minutes to fall asleep.
Is 6 hours of sleep enough?
For most adults, no. The recommended range is 7–9 hours a night.