Keep a steady schedule
Similar bed and wake times help your body expect the next cycle. Weekday–weekend swings make mornings harder.
Sleep cycle calculator
Wake between cycles.
Feel human again.
Plan bedtimes and wake-up times around 90-minute sleep cycles so you rise from light sleep — not mid-dream fog.
Default 14 minutes. Most people need a short wind-down before the first cycle starts.
Ready for morning? Use Heavy Sleeper’s rising sound, screen light and wake-up task so finishing a cycle actually sticks.
Set Alarm with Heavy SleeperLearn the basics
How this sleep calculator works
How do 90-minute sleep cycles work?
Sleep usually moves through light sleep, deep sleep and REM in roughly 90-minute cycles. Waking near the end of a cycle often feels clearer than waking mid-cycle, when deep sleep or REM can leave you groggy. This calculator lines up 3–6 full cycles plus your fall-asleep time.
Why use a sleep cycle calculator?
It turns “I need about 8 hours” into concrete bedtimes or wake times. Ideal windows are 5–6 cycles (about 7.5–9 hours). Four cycles can still work on a busy night. Three cycles is an emergency power nap, not a full night.
What if I am a heavy sleeper?
Even with perfect timing, some mornings need more than a gentle chime. Pair this calculator with Heavy Sleeper’s sound, light and a short wake-up task, and keep your phone’s regular alarm as backup.
Dim screens before bed
Bright light late at night can delay sleep onset. Give yourself the latency you set — then put the phone down.
Plan the wake-up
Know which result card you will use, set the alarm once, and avoid mid-night renegotiation.