How the tools work
Sleep calculator methodology
The calculators use transparent time arithmetic and adjustable assumptions. They do not measure your sleep stages.
Last reviewed: by the Sleep Better Timer editorial team.
Bedtime formula
bedtime = wake time - fall-asleep estimate - cycle estimate × cycles
The tool shows 6, 5, 4, and 3 cycle options. Longer options appear first because they provide more sleep opportunity.
Wake-up formula
wake time = bedtime + fall-asleep estimate + cycle estimate × cycles
The sleep-now version reads the current local time from your device after the page loads. Calculations wrap across midnight and display the calendar date when needed.
Why 90 minutes is adjustable context, not a promise
Real sleep cycles vary between people and across a night. We use 90 minutes as a familiar planning approximation, not as a measurement of your individual sleep stages.
Fall-asleep time
The default is 15 minutes, with 10, 20, and 30 minute alternatives. This is a user-controlled estimate. The website does not determine how long you actually take to fall asleep.
What the result means
A result is a possible planning window. It does not predict sleep quality, diagnose a sleep issue, or guarantee that waking at that time will feel easier.
Read our editorial policy for sourcing and correction standards.
Sources