Sleep Calculator

Find your optimal bedtime and wake-up time based on 90-minute sleep cycles.

1Bedtime

What time are you going to bed?

:(24h)

Time to fall asleep

Recommended Wake-up Times

5:15 AM

6h (4 cycles)Minimum

6:45 AM

7h 30m (5 cycles)Recommended

8:15 AM

9h (6 cycles)Optimal

Based on 90-min cycles · Includes 15min to fall asleep · Adults need 7-9 hours (5 cycles)

2Recommended Sleep by Age

Age Group	Sleep	Cycles
Newborn (0-3 mo)	14-17h	-
Infant (4-11 mo)	12-15h	-
Toddler (1-2 yr)	11-14h	-
Preschool (3-5 yr)	10-13h	-
School age (6-13 yr)	9-11h	6-7
Teen (14-17 yr)	8-10h	5-6
Young adult (18-25)	7-9h	5-6
Adult (26-64)	7-9h	5-6
Older adult (65+)	7-8h	5

Source: National Sleep Foundation

Sleep Guide

Understanding Sleep Cycles: Sleep consists of repeating ~90-minute cycles of NREM stages 1-3 and REM sleep. Deep sleep (NREM 3) is for physical recovery, while REM sleep handles memory consolidation and learning. Waking at the end of a cycle (after REM) feels refreshing; waking during deep sleep causes grogginess.

Improving Sleep Quality: The most important factor is a consistent sleep schedule - go to bed and wake up at the same time daily. Avoid caffeine, alcohol, and heavy meals 2 hours before bed. Keep your bedroom dark and cool (65-68°F / 18-20°C). Replace screen time with reading or stretching in the last hour before sleep.

Effects of Sleep Deprivation: Chronic sleep deprivation is linked to reduced concentration, weakened immunity, obesity, and increased cardiovascular risk. Sleeping under 6 hours for 2+ weeks causes cognitive decline similar to 48 hours without sleep. Weekend catch-up sleep does not fully repay sleep debt.

Frequently Asked Questions

Q. What is a sleep cycle?

A. A sleep cycle is approximately 90 minutes of alternating NREM and REM sleep. You go through 4-6 cycles per night. Waking at the end of a cycle feels more refreshing than waking mid-cycle.

Q. How many hours of sleep do adults need?

A. The National Sleep Foundation recommends 7-9 hours for adults aged 18-64, and 7-8 hours for those 65+. Five 90-minute cycles (7.5 hours) is often considered the sweet spot.

Q. Why does the calculator account for falling asleep time?

A. It typically takes 10-20 minutes to fall asleep. Without this buffer, sleep cycle timing would be off, causing you to wake during deep sleep and feel groggy instead of refreshed.

✓Updated for 2026Last reviewed October 6, 2026See what changed

Written and reviewed by Taeyang Kim · Rates and thresholds are taken directly from the official notices of Korea's National Tax Service, National Pension Service, National Health Insurance Service, Ministry of Employment and Labor, and Minimum Wage Commission. Results are non-binding estimates for reference only and may differ from the actual amount depending on your circumstances. Found a mistake? Tell us through Contact.