Sleep Calculator

Wake up refreshed, not groggy. Pick a wake time or bedtime and get the optimal sleep and wake windows aligned to 90-minute sleep cycles.

Healthy BMI18.5 – 24.9

Daily Calories2,000 – 2,500(avg adult)

Sleep Cycle90 min(per cycle)

Wake-up time

Go to bed at one of these times to wake up feeling refreshed:

9:45 PM

6 cycles · 9h of sleep

Optimal

11:15 PM

5 cycles · 7.5h of sleep

Good

12:45 AM

4 cycles · 6h of sleep

Minimum

6 cycles · 9h sleep

6 × 90 min + 15 min fall-asleep = 555 min

07:00 − 555 min

= 9:45 PM

Optimal (9h total window)

5 cycles · 7.5h sleep

5 × 90 min + 15 min fall-asleep = 465 min

07:00 − 465 min

= 11:15 PM

Good (7.5h total window)

4 cycles · 6h sleep

4 × 90 min + 15 min fall-asleep = 375 min

07:00 − 375 min

= 12:45 AM

Minimum (6h total window)

Key insight

A 90-minute cycle is the core unit of restorative sleep — 5 cycles (7.5h) is the NSF sweet spot for most adults. The 15-minute fall-asleep buffer prevents the most common mistake: lying down at the target time instead of before it. Waking mid-cycle triggers sleep inertia; waking at cycle's end leaves you alert even if total hours are the same.

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How sleep cycles work

Each sleep cycle lasts about 90 minutes and moves through light sleep, deep sleep, and REM. Waking up at the end of a cycle — rather than in the middle — is what leaves you feeling alert instead of groggy. This calculator adds 15 minutes to account for the average time it takes to fall asleep.

Recommended hours by age (NSF)

Newborn (0–3 mo)14–17h

Infant (4–11 mo)12–15h

Toddler (1–2 yr)11–14h

Preschool (3–5)10–13h

School age (6–13)9–11h

Teen (14–17)8–10h

Adult (18–64)7–9h

Older adult (65+)7–8h