Sleep Calculator
Find the best times to wake up based on sleep cycles.
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How It Works
Calculates the number of complete 90-minute sleep cycles in a given number of hours. Each sleep cycle progresses through light sleep, deep sleep, and REM. Waking between cycles (not during) feels more refreshing.
Formula
Wake times at 90-min cyclesQuick Reference
Common calculations — results you can verify instantly.
6 hours sleep
360/90 min
4 sleep cycles
7.5 hours sleep
450/90 min
5 sleep cycles (optimal)
9 hours sleep
540/90 min
6 sleep cycles
Tips & Shortcuts
Best sleep durations: 6h (4 cycles), 7.5h (5 cycles), 9h (6 cycles).
Wake at the end of a cycle (7.5h) rather than mid-cycle (7h) for better alertness.
Sleep quality matters as much as quantity. Dark, cool, quiet room optimizes sleep.
Common Mistakes
Ignoring sleep cycle timing when setting alarms
Set alarm to end of a cycle. 7.5h feels better than 8h if the extra 30min is mid-cycle deep sleep.
Thinking more sleep is always better
Consistently sleeping 9+ hours is associated with health risks similar to under-sleeping.
Frequently Asked Questions
Most adults complete 4-6 cycles per night. 5 cycles (7.5 hours) is considered optimal for most adults.
Stage 1-2: Light sleep, easy to wake. Stage 3: Deep sleep, body repair. Stage 4 (REM): Dreams, memory consolidation. Each cycle takes ~90 minutes.
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