Sleep Calculator
Plan bedtime or wake-up ranges from NIH-described 80–100 minute sleep cycles without promising sleep quality, stages or medical outcomes. Sensitive inputs stay in your browser.
Three planning ranges use 4–6 cycles of 80–100 minutes plus the entered fall-asleep allowance.
Context matters.
- The ranges are scheduling aids, not medical advice or a claim that waking between cycles guarantees feeling rested.
Sources & scope
The calculation guide and this source trail show what the result means, where the rule came from and when it was last reviewed. This is source-and-calculation QA, not a claim of medical, legal, tax or other professional review; time-sensitive decisions still belong with the linked authority.
A visible path from input to answer.
Plan bedtime or wake-up ranges from NIH-described 80–100 minute sleep cycles without promising sleep quality, stages or medical outcomes. The page keeps the calculation scope and its limits beside the result so the output can be checked, copied or revisited.
- Read the record. The calculator uses Plan from, Planning date, Wake-up time, Bedtime and Planning cycles and 3 additional fields supplied in the form.
- Apply the scope. It applies the Personal sleep scheduling using an NIH-described 80–100 minute cycle range — no sleep-quality, stage or medical prediction reference and the explicit date, unit and counting conventions shown in the result.
- Expose the checkpoints. Intermediate rows, warnings and timeline events stay visible; the emphasized row identifies the primary checkpoint when one exists.
Three planning ranges use 4–6 cycles of 80–100 minutes plus the entered fall-asleep allowance.
- 5-cycle bedtime windowAug 30, 2026 · 10:25 PM – Aug 31, 2026 · 12:05 AM
Calculation purpose: Plan bedtime or wake-up ranges from NIH-described 80–100 minute sleep cycles without promising sleep quality, stages or medical outcomes. This is a conditional reference output; the linked source and the situation-specific facts control the decision.
Calendar inputs use plain year-month-day semantics. Leap days, month ends, date-pair order and unsupported dates are checked before the result is shown.
Rule set 1.1.0 · Last reviewed 2026-08-23 · Next review due 2027-02-23. The source panel below contains the linked evidence.
What to know before using the result.
What time should I go to bed?
Enter a wake-up time to see several bedtime ranges based on four to six cycles of 80–100 minutes plus your fall-asleep allowance.
Are sleep cycles exactly 90 minutes?
No. NIH says the cycle starts over about every 80 to 100 minutes, so CalcSpan uses a range instead of presenting 90 minutes as a fixed biological rule.
Does waking between cycles guarantee feeling rested?
No. The output is a clock-planning aid and does not predict sleep stages, quality, individual need or a medical outcome.