How the Sleep Cycle Calculator Works

Rezumat

Sleep occurs in repeating cycles of approximately 90 minutes, each progressing through light sleep (N1, N2), deep sleep (N3), and REM sleep. Waking at the end of a complete cycle — rather than mid-cycle — is associated with feeling more alert and refreshed. This calculator suggests optimal bedtimes or wake-up times aligned to complete 90-minute cycles, adjusted for the time it takes you to fall asleep.

Cum funcționează

The calculator operates in two modes:

1. “When to sleep” mode — given a desired wake-up time, it calculates bedtimes that allow you to complete 4, 5, or 6 full sleep cycles before your alarm
2. “When to wake” mode — given a planned bedtime, it calculates wake-up times aligned to the end of complete sleep cycles

Both modes account for sleep onset latency — the time between getting into bed and actually falling asleep. The average healthy adult takes 10–20 minutes to fall asleep (Ohayon et al., 2004). The calculator defaults to 15 minutes.

Formula

For wake-up mode, the formula is reversed:

Sleep cycle ratings

Exemplu rezolvat

Intrări explicate

• Mode — choose between “When to sleep” (you set the wake-up time) and “When to wake” (you set the bedtime)
• Hour and minute — the target time (wake-up time in bedtime mode, or bedtime in wake-up mode)
• Time to fall asleep — your estimated sleep onset latency (0–45 minutes, default 15)

Rezultate explicate

• Best suggestion — the time for 5 complete cycles (7h 30m), highlighted as the hero metric
• All suggestions — times for 4, 5, and 6 complete cycles, colour-coded green (recommended: 5–6 cycles) or amber (acceptable: 4 cycles)
• Sleep duration — total sleep time for each suggestion (not including latency)

Ipoteze și limitări

• 90 minutes is an approximation. Real sleep cycles vary from 70–120 minutes, with the first cycle typically shorter and later cycles longer (StatPearls, NCBI). The 90-minute figure is the industry-standard average used by all major sleep calculators.
• Sleep onset latency varies. The same person may take 5 minutes one night and 30 minutes the next. The calculator uses your estimate, not a measured value.
• Night-time awakenings are normal and not accounted for. Most adults briefly wake 2–3 times per night without remembering.
• Sleep architecture changes with age. Older adults tend to have less deep sleep and more fragmented sleep.
• This is a planning tool, not a medical device. If you regularly take over 30 minutes to fall asleep, or consistently feel unrefreshed despite adequate sleep time, consult a healthcare provider.

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