Sleep Cycle Calculator
Calculate ideal bedtime and wake-up times based on 90-minute sleep cycles
Wake-up time
Calculation includes 14 min average time to fall asleep.
Go to sleep at
Set a time and click Calculate
Sleep Cycles
Each sleep cycle lasts about 90 minutes and moves through light, deep (N3), and REM sleep stages.
Why 6 Cycles?
Most adults feel their best after 7.5–9 hours (5–6 full cycles). Waking in the middle of a cycle causes grogginess.
Fall Asleep Time
The average person takes about 14 minutes to fall asleep. This buffer is included in every calculation automatically.
Frequently asked questions
How long is a sleep cycle?
One sleep cycle lasts approximately 90 minutes and consists of four stages: N1 (light sleep), N2 (deeper light sleep), N3 (deep/slow-wave sleep), and REM (dream sleep). A full night typically includes 4–6 complete cycles.
Why is waking between cycles important?
Waking in the middle of deep sleep (N3) causes sleep inertia — the grogginess and disorientation that can last 30+ minutes. Waking at the natural end of a cycle, when sleep is lightest, lets you feel alert immediately.
Why does the calculator add 14 minutes?
Sleep onset latency (the time it takes to actually fall asleep after lying down) averages about 14 minutes for healthy adults. The calculator adds this buffer so the cycle timing starts from when you are actually asleep, not just in bed.
How many hours of sleep do I need?
The CDC recommends 7–9 hours for adults (18–60 years). This corresponds to 5–6 complete 90-minute cycles. Our calculator marks 6 cycles (9 hours of actual sleep + 14 min = 9h 14m in bed) as 'Recommended', but 5 cycles (7.5h) is also healthy for most people.