Sleep Calculator
Find the best bedtime or wake-up time based on 90-minute sleep cycles. Wake up refreshed by timing your alarm to the end of a cycle.
Go to sleep at…
10:09 AM
7 cycles · 10.5 hours of sleep
11:39 AM
6 cycles · 9 hours of sleep
01:09 PM
5 cycles · 7.5 hours of sleep
02:39 PM
4 cycles · 6 hours of sleep
Most adults need 5–6 complete cycles (7.5–9 hours) for optimal rest.
How to Use
- 1
Choose your mode
Select Wake-up time if you know when you need to wake, or Bedtime if you know when you want to sleep.
- 2
Enter the time
Type your target wake-up time or bedtime. Click Now to use the current time.
- 3
Pick the best option
Choose from the recommended sleep times — 6 sleep cycles (9 hours) or 5 cycles (7.5 hours) are ideal.
How It Works
This calculator finds the optimal bedtime or wake-up time based on 90-minute sleep cycles, so your alarm lines up with the end of a cycle rather than interrupting deep sleep mid-cycle.
Why sleep cycles matter for how rested you feel
Sleep progresses through roughly 90-minute cycles of light sleep, deep sleep, and REM sleep. Waking up at the boundary between cycles (when sleep is naturally lightest) tends to feel more refreshing than waking up mid-cycle during deep sleep, which is why timing your wake-up to align with a cycle boundary rather than just picking a round number of hours can improve how rested you feel.
The two calculation modes
If you know your target wake-up time, the calculator works backward in 90-minute increments to suggest bedtimes that align with a full number of cycles. If you know your bedtime instead, it works forward to suggest wake-up times that land on a cycle boundary — plus it adds roughly 15 minutes to any bedtime suggestion to account for the average time it takes to actually fall asleep.
Examples
Working backward from a wake-up time
If you need to wake up at 6:30 AM, going to bed at 9:15 PM hits exactly 6 full cycles (9 hours) accounting for the 15-minute fall-asleep buffer — one of several cycle-aligned options the calculator would present.
Working forward from a bedtime
Going to bed at 11:00 PM (plus the 15-minute buffer), waking at 6:00 AM would align with 5 full cycles (7.5 hours) — often the recommended minimum for adults.
Common Use Cases
- Choosing a bedtime that lines up with a natural wake-up time for a specific morning schedule
- Choosing an alarm time that lands at the end of a sleep cycle rather than mid-cycle for an already-set bedtime
- Understanding how many full sleep cycles a given amount of sleep actually represents
Tips
- Most adults need 5-6 full cycles (7.5-9 hours) for adequate rest — 4 cycles (6 hours) is generally considered a minimum, not an ideal target, even if it aligns with a cycle boundary.
- Individual sleep cycle length varies somewhat from the standard 90-minute average, so treat cycle-aligned suggestions as a helpful guideline to experiment with rather than an exact science guaranteed to work identically for everyone.
Frequently Asked Questions
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