Sleep Need Calculator
Plan a bedtime from your wake time and desired sleep duration.
Inputs
Result
Suggested bedtime
22:45
8 hr sleep + 15 min to fall asleep
Visual breakdown
Bedtime window start
22:30
Start winding down
Target bedtime
22:45
Window end
23:00
Latest to sleep
Wake time
07:00
Formula
Bedtime = wake time − sleep duration − 15 min (to fall asleep). Window is ±15 min around bedtime.
Example
Wake 07:00, 8 hr sleep → bedtime 22:45 (window 22:30–23:00).
Common examples
Wake 7:00, 8 hr sleep
Aim for bed by 22:45 (with 15 min wind-down).
Wake 6:00, 7.5 hr sleep
Aim for bed by 22:15.
Shift work
Pick any wake time — the math is the same.
Frequently asked
How much sleep do adults need?
Most adults function best on 7–9 hours. Teens often need 8–10. Children need more.
Why subtract 15 minutes?
Healthy adults typically fall asleep in 10–20 minutes. The buffer keeps the actual sleep duration on target.
What about sleep cycles?
Cycles average ~90 minutes, but they vary night to night. Aim for total hours rather than chasing exact cycle counts.
Does this account for shift work?
Yes — any wake time works. Consistent wake/sleep times matter more than the specific clock hour.
People also calculate
More health →Educational planner only — not medical advice.