Sleep Calculator
Wake up refreshed by timing your sleep in 90-minute cycles.
Go to bed at one of these times
Highlighted times give 5–6 cycles (7.5–9 hours), the recommended range for most adults.
Time your sleep around 90-minute cycles
Sleep happens in cycles of roughly 90 minutes, moving from light sleep into deep sleep and REM, then back to light sleep. Waking at the end of a cycle — rather than in the middle of deep sleep — tends to leave you feeling more refreshed and less groggy. This calculator works backward or forward from your chosen time to suggest moments that land at the end of a full cycle.
Pick a mode: enter the time you need to wake up and the tool lists the best bedtimes, or enter when you plan to go to bed and it lists the best times to set your alarm. Each suggestion assumes about 15 minutes to fall asleep and is spaced one full cycle (90 minutes) apart, so you can choose how many cycles fit your night.
Most adults do best with five or six complete cycles, which is about 7.5 to 9 hours of sleep. Those options are highlighted. Fewer cycles are offered for short nights or naps, but they are not a substitute for regular, sufficient sleep.
FAQ
Why 90 minutes per cycle? A typical adult sleep cycle averages around 90 minutes, though it varies from roughly 80 to 110 minutes between people and across the night. The calculator uses 90 minutes as a practical average.
Why add 15 minutes? Most people take about 10 to 20 minutes to actually fall asleep after lying down. The tool adds 15 minutes so the cycle count reflects time asleep, not time in bed.
How many cycles should I aim for? Five to six cycles (7.5 to 9 hours) suits most adults. Waking at the end of any cycle is generally easier than waking mid-cycle, even if the total is a little shorter.
Is this medical advice? No. This is a simple timing aid based on average cycle length. If you regularly struggle with sleep, talk to a healthcare professional.