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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.

Where this fits

❤️ HealthHouseholds

This tool sits in the health domain and connects best with the next tools in that decision lane.

Healthy BMI18.5 – 24.9
Daily Calories2,000 – 2,500
Sleep Cycle90 min

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
1

6 cycles · 9h sleep

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

07:00 − 555 min

= 9:45 PM

Optimal (9h total window)

2

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)

3

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.

#ShowYourWork

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

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