Sleep Calculator

The Sleep Calculator helps you find the ideal bedtime or wake-up time based on your body's natural sleep cycles. Waking up at the end of a complete cycle — instead of in the middle of one — is what makes the difference between feeling groggy and feeling refreshed.

Sleep happens in 90-minute cycles, each consisting of light sleep, deep sleep (slow-wave), and REM sleep. Interrupting a cycle mid-way — particularly during deep sleep — is what causes that heavy, foggy feeling known as sleep inertia.

This calculator adds 15 minutes to fall asleep (the average for most adults) and calculates four optimal times based on 4, 5, 6, and 7 complete cycles:

• 4 cycles (6 hours) — Minimum viable sleep. Fine occasionally, not sustainable long-term.
• 5 cycles (7.5 hours) — Optimal for most adults. The recommended sweet spot.
• 6 cycles (9 hours) — Great for recovery days, illness, or sleep debt repayment.
• 7 cycles (10.5 hours) — Extended recovery sleep.

Example

You need to wake up at 7:00 AM. When should you go to sleep?

Subtracting 15 min (to fall asleep) + 7.5 hours (5 cycles): go to bed at 11:15 PM.

Other options: 12:45 AM (4 cycles, 6h) or 9:45 PM (6 cycles, 9h).

The 11:15 PM bedtime gives 5 complete 90-minute cycles — the optimal amount for most adults. You'd be in light sleep around 7:00 AM, making the alarm far less jarring than if it caught you mid-deep-sleep cycle.