😴 Sleep Calculator
Enter when you need to wake up — or when you're going to bed — and get times that fall between 90-minute sleep cycles, so you wake up feeling less groggy.
How to use the sleep calculator
- Wake-up time → bedtime: enter when your alarm goes off and get the times to go to bed for 3 to 6 full sleep cycles.
- Bedtime → wake-up time: enter when you're getting into bed (now, or later tonight) and get alarm times that land at the end of a cycle.
- Nap: enter when you lie down for 10-, 20- and 30-minute naps, a full-cycle nap, and a coffee nap.
The calculator adds the time it takes you to fall asleep (15 minutes by default — the typical range for healthy adults is about 10–20 minutes).
How it works
bedtime = wake-up time − (number of cycles × cycle length) − time to fall asleep. During the night you move through light sleep, deep sleep and REM sleep in cycles averaging about 90 minutes. Waking at the end of a cycle, when sleep is lighter, tends to feel easier than being jolted out of deep sleep. Real cycles vary from roughly 70 to 120 minutes between people and across the night, so if you still wake up groggy after a few days, try an 80- or 100-minute cycle length.
Example: waking up at 7:00 AM
| Cycles | Sleep | Go to bed at |
|---|---|---|
| 6 | 9h | 9:45 PM |
| 5 | 7h 30m | 11:15 PM |
| 4 | 6h | 12:45 AM |
| 3 | 4h 30m | 2:15 AM |
How much sleep do you need?
| Age | Recommended sleep per 24 hours |
|---|---|
| Teens 13–18 | 8–10 hours |
| Adults 18–60 | 7 or more hours |
| Adults 61–64 | 7–9 hours |
| Adults 65+ | 7–8 hours |
These are the CDC's guidelines based on American Academy of Sleep Medicine recommendations. That's why 5 cycles (7.5 hours) and 6 cycles (9 hours) are marked as recommended; 4 cycles (6 hours) is a fallback for a short night. More important than hitting a cycle exactly is waking up at the same time every day, weekends included.
Better-sleep tips
- Get daylight soon after waking and keep the bedroom dark, quiet and cool.
- Avoid caffeine for about 6 hours before bed and heavy meals or alcohol close to bedtime.
- Keep naps short (10–20 minutes) and before mid-afternoon so they don't steal from night sleep.
For general lifestyle reference only, not medical advice. If you snore loudly, stop breathing during sleep or feel very sleepy during the day despite enough sleep, talk to a doctor or sleep specialist.