Health
Sleep Calculator
Find the best bedtimes or wake-up times based on 90 minute sleep cycles. Includes a 15 minute fall-asleep buffer.
Find your best wake-up times
Suggested wake-up times
3:15 AM
3 cycles, 4h 30m
4:45 AM
4 cycles, 6h
Ideal range
6:15 AM
5 cycles, 7h 30m
Ideal range
7:45 AM
6 cycles, 9h
Ideal range
9:15 AM
7 cycles, 10h 30m
10:45 AM
8 cycles, 12h
Based on a 15-minute fall-asleep buffer and 90-minute sleep cycles. Waking at the end of a cycle helps you feel more refreshed.
Frequently Asked Questions about the Sleep Calculator
What is a 90-minute sleep cycle?
One complete sleep cycle lasts about 90 minutes and passes through light sleep, deep sleep, and REM. The calculator uses this 90-minute figure to space every suggested bedtime or wake-up time. Most adults do best with 5 or 6 full cycles (7.5 to 9 hours) per night, though the calculator shows options from 3 cycles (4h 30m) up to 8 cycles (12h).
What is REM sleep?
REM (Rapid Eye Movement) is the stage when most dreaming happens. It supports memory consolidation, learning, and emotional regulation. REM periods get progressively longer across the night, so cutting sleep short cuts the most REM, even if total sleep time looks adequate.
Why should I wake at the end of a sleep cycle?
Deep sleep (slow-wave sleep) is hardest to wake from. Interrupting it causes sleep inertia, that heavy, disoriented feeling that can last 20-30 minutes. The end of a cycle is the lightest sleep stage, so timing your alarm there means you surface more naturally and feel alert faster, even if total sleep is slightly shorter.
Why does the calculator add 15 minutes?
The calculator assumes a 15-minute sleep-onset window, roughly the average time a healthy adult takes to fall asleep once in bed. Every suggested time already accounts for this buffer, so the result reflects when you need to get into bed, not just when the math hits a cycle boundary.
What is sleep debt?
Sleep debt is the cumulative difference between the sleep your body needs and what it actually gets. Even a one-hour nightly shortfall adds up, so after a week you carry roughly the equivalent of an all-nighter. You can reduce mild debt with extra sleep on weekends, but chronic debt affects focus, metabolism, and immune function in ways short-term recovery does not fully reverse. Aim for 5 to 6 full cycles (7.5 to 9 hours) on most nights.