A clearer way to plan tonight
Plan a bedtime or wake-up time in seconds. See the assumptions whenever you need them.
Includes 15 minutes to fall asleep.
Quick answer
Use Wake at mode to estimate a bedtime, or Sleep at mode and Sleep now mode to estimate a wake-up time. SleepPrism includes your selected time-to-fall-asleep allowance and uses 90 minutes as a planning value, not a promise of cycle length. It shows a primary option with 7 hours 30 minutes of estimated sleep and a longer 9-hour option.
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The calculator adds or subtracts your selected time-to-fall-asleep allowance, then applies estimated sleep-duration options. The 15-minute default is an adjustable planning assumption, not a measurement of how long you will take to fall asleep. See the full methodology.
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The NHLBI describes sleep cycles as restarting about every 80 to 100 minutes. SleepPrism uses 90 minutes as a simple value within that range. A clock-based calculator cannot measure your brain activity or identify a future sleep stage.
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The result does not measure sleep quality, alertness, health, or your individual sleep need, and it cannot promise that you will feel rested. The calculation runs on your device without requiring an account. Review our sources and evidence standards.
Limits and safety
Adults are generally advised to get at least seven hours of sleep, while individual needs and sleep quality still matter. Use the sleep-needs-by-age guide for broader context rather than treating a calculated time as a personal recommendation.
Do not use this calculator to decide whether you are safe to drive, work, supervise someone, or operate machinery. If you feel dangerously sleepy, stop the risky activity. The NHLBI explains how sleep deficiency can affect driving and daily functioning.
If you regularly have trouble sleeping or continue to feel sleepy or tired after enough time in bed, speak with a qualified healthcare professional. This follows the CDC's general sleep guidance; SleepPrism does not diagnose or treat sleep problems.
Claims on this page were checked against the CDC and the National Heart, Lung, and Blood Institute. The calculation rules and their limitations are documented separately in our methodology and source list.