Protect the last hour
Dim lights and skip doomscrolling so your chosen latency is realistic.
Sleep cycle calculator
Time your sleep.
Wake with a better sound.
Use 90-minute cycles to pick bedtimes or wake-up times, then download a free alarm sound — or set a full wake session on Heavy Sleeper.
Default 14 minutes. Adjust if you usually fall asleep faster or slower.
Need more than a ringtone? Heavy Sleeper combines rising sound, screen light and a wake-up task. Or pick a free sound for your phone’s Clock app.
Set Alarm with Heavy SleeperLearn the basics
How sleep cycles work
A quick guide so the color-coded cards make sense tonight.
How do 90-minute sleep cycles work?
Most nights move through light sleep, deep sleep and REM in cycles of about 90 minutes. Waking near the end of a cycle often feels clearer than waking mid-cycle. This tool adds your fall-asleep latency, then shows 3–6 cycle options.
Why use a sleep calculator?
It turns vague “8 hours of sleep” into specific times. Green cards (5–6 cycles) are the sweet spot. Yellow is a workable minimum. Red is for emergency power naps only.
What should heavy sleepers do after calculating?
Choose a wake time, then either install a WakeUpSounds ringtone or open Heavy Sleeper for sound, light and a short task. Always keep a system alarm as backup. Read why you might sleep through your alarm, why you feel groggy after waking and how to wake up early.
Test the sound once
Preview your alarm at the volume you will actually use tomorrow morning.
Same wake window
Repeating a similar wake time helps your body finish cycles more predictably.