Sleep Calculator

Plan wake-up or bedtime using sleep cycles, target sleep duration, and daily routine assumptions.

Suggested bedtime

23:15

7.5 hr of sleep cycles

Wake time

07:00

Target wake-up time

Cycles

90 minutes each

Fall-asleep buffer

15 min

Time before sleep starts

Sleep cycle inputs

Plan bedtime from wake time, sleep cycles, and fall-asleep buffer.

Wake hour

Wake minute

Sleep cycles

Cycle length

min

Fall-asleep buffer

min

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What is the sleep calculator?

This calculator uses the 90-minute sleep cycle to recommend bedtime or wake-up time. It applies a default 15-minute sleep latency and shows 4 to 6 cycle options so users can avoid waking during deep sleep when possible.

A sleep cycle alternates through NREM and REM sleep. Waking near the end of a cycle can improve cognitive function and mood by up to about 30% compared with waking from deep sleep.

Sleep stages and cycles

Stages inside one cycle

Stage 1 sleep onset lasts about 5 to 10 minutes.
Stage 2 light sleep lasts about 10 to 25 minutes.
Stage 3 deep sleep lasts about 20 to 40 minutes and is important for growth hormone release and immunity. Waking here causes strong grogginess.
REM sleep lasts about 10 to 60 minutes, is associated with dreams, memory, and learning, and becomes longer later in the night.

How many cycles to target

Four cycles equal about 6 hours of sleep and may be acceptable briefly, but it is not the long-term adult target.
Five to 6 cycles equal about 7.5 to 9 hours and are ideal for most adults.
If sleep latency exceeds 30 minutes repeatedly, improve light, noise, caffeine timing, room temperature, and pre-sleep routines instead of only shifting alarm time.

Age recommendations and sleep debt

Recommended sleep by age

Newborn 0 to 3 months: 14 to 17 hours.
Infant 4 to 11 months: 12 to 15 hours.
Toddler 1 to 2 years: 11 to 14 hours.
Preschool 3 to 5 years: 10 to 13 hours.
School age 6 to 13 years: 9 to 11 hours.
Teen 14 to 17 years: 8 to 10 hours.
Young adult 18 to 25 and adult 26 to 64: 7 to 9 hours.
Senior 65 and older: 7 to 8 hours.

Sleep debt recovery

Being short 1 hour per day creates 7 hours of sleep debt in a week.
Sleep debt can reduce cognition, weaken immunity, affect mood, increase weight-gain risk, and raise chronic-disease risk.
Recover gradually. Weekend extra sleep of 1 to 2 hours can help, naps should stay 20 minutes or less, and weekend wake time should stay within about 1 hour of weekdays.