Sleep Calculator: Bedtime and Wake-Time Planner
Plan bedtime or wake time from a chosen sleep duration and time to fall asleep. Avoid treating every sleep cycle as exactly 90 minutes.
Your inputs
Choose the units and assumptions that match your data. Example inputs are illustrative.
Your result
Enter your values, then choose Calculate.
Results are calculated in your browser. Display rounding does not change the underlying calculation.
Calculation breakdown
Method, assumptions and worked example
How it works
For a wake-time plan, subtract sleep duration and sleep-onset time from the wake time. For a bedtime plan, add them to the bedtime. The result identifies whether it falls on the previous, same or next day.
Worked example
To wake at 07:00 after eight hours asleep with 15 minutes to fall asleep, plan to go to bed at 22:45 the previous day.
Using the result
Adults generally need 7–9 hours. Sleep cycles vary, so scheduling exact 90-minute multiples cannot guarantee an easy wake-up. This is a clock planner without a date or timezone; daylight-saving changes are not applied. Persistent sleep problems warrant professional advice.
Frequently asked questions
Why not promise the end of a 90-minute cycle?
NHLBI describes cycles of roughly 80–100 minutes; an individual cycle is not a fixed timer.
Does the result include falling-asleep time?
Yes. That time is added to the planned duration in bed, separate from time asleep.
Method review and references
Formula and content reviewed on 10 October 2026. Worked examples are hypothetical. Methods and assumptions are explained on each page. Health estimates are not clinical measurements; symbolic tools are for entertainment.