Sleep Calculator
Sleep runs in roughly 90-minute cycles. Waking at the end of a cycle feels easier. Pick a wake time or a bedtime and we'll suggest the times that line up.
Aim for 5 to 6 cycles (about 7.5 to 9 hours). The bold options are the sweet spot for most adults.
How the sleep calculator works
A sleep cycle averages 90 minutes. We count whole cycles and add your fall-asleep time so you wake at the end of a cycle, not the middle of deep sleep:
Bedtime = wake time - (cycles x 90 min) - fall-asleep time
Wake time = bedtime + fall-asleep time + (cycles x 90 min)
Most adults need 7 to 9 hours (5 to 6 cycles). Consistency matters as much as the total.
Source: sleep-cycle physiology; NSF/CDC sleep duration guidance.
Frequently asked questions
Why 90-minute sleep cycles?
A full sleep cycle averages about 90 minutes, moving through light, deep and REM stages. Waking at the end of a cycle tends to feel easier than being jolted out of deep sleep.
How much sleep do I need?
Most adults need 7 to 9 hours (five to six cycles); teenagers 8 to 10; adults 65+ around 7 to 8. Consistency matters as much as total hours.
Why do I feel worse after more sleep sometimes?
Waking in the middle of deep sleep causes grogginess (sleep inertia), even after a long night. Aligning to whole cycles helps avoid it.
What is sleep latency?
It is how long it takes you to fall asleep, about 15 minutes on average. We add it so the cycles start when you are actually asleep.
Medical disclaimer: This calculator is for general information and education only. It is an estimate, not medical advice, diagnosis or treatment. Always talk to your doctor or midwife about your health and any decisions.