Trust and transparency
Methodology
How SleepPrism calculates planning estimates and communicates their limitations.
Last reviewed: August 11, 2026
What the calculator does
The calculator starts with a time you provide, adds or subtracts an allowance for falling asleep, and applies estimated sleep-duration options. All calculation inputs stay in your browser in the current version.
Default assumptions
The default allowance for falling asleep is 15 minutes. The planning options use 90 minutes as a simple cycle estimate and prioritize an estimated 7 hours 30 minutes of sleep, with a longer 9-hour option. You can adjust the time-to-fall-asleep assumption.
Why these are estimates
Sleep cycles are not fixed clocks. Their length varies between people and during the night. SleepPrism cannot know which sleep stage you will be in at a future time and does not promise that a suggested time will make waking easier.
Date and time handling
Scheduled times resolve to the next local occurrence on your device. The calculation uses elapsed time so that date boundaries and daylight-saving changes can be handled consistently.
Review and change control
Calculation rules and source tables are versioned. Material changes require tests, an editorial review, an updated review date, and a correction note when a published conclusion changes.