About
Four calculators built on published ranges, with the assumptions printed next to the result.
What this site is
Four small calculators about sleep: one turns a wake-up time into candidate bedtimes (or the reverse), one looks up a recommended duration by age, one adds up a week of short nights, and one times a nap. All run in the browser; nothing is stored and there is no account.
The method
| Quantity | Assumption | Where it comes from |
|---|---|---|
| Sleep cycle | 90 minutes | Population average; individual cycles run 80–120 minutes |
| Cycles offered | 6, 5 or 4 | 9, 7.5 and 6 hours of sleep |
| Sleep-onset time | 15 minutes, adjustable | Typical adult value; the field is there because yours will differ |
| Recommended duration | Age bands | American Academy of Sleep Medicine and Sleep Foundation ranges |
| Sleep debt | Sum of nightly shortfalls against a target | Arithmetic only; recovery is not 1:1 (see the calculator page) |
| Nap length | 20, 30 or 90 minutes after sleep onset | Chosen to match “no deep sleep”, “inertia risk” and “one full cycle”; not a prescription |
The wake time is the fixed point, because that is the signal the circadian system entrains to. Counting backwards from it produces a schedule that is stable; counting forwards from bedtime produces one that drifts with how tired you happen to feel.
What it cannot do
- Measure your cycles. That needs polysomnography or a wearable, and even wearables infer rather than measure stages.
- Fix a sleep disorder. Insomnia, apnoea and restless legs are clinical problems; a bedtime calculator is not a treatment.
- Account for sleep quality. Two nights with the same duration can be very different in how they feel.
- Replace individual advice. Pregnancy, shift work, medication and age all move the target.
Not medical advice. These pages do arithmetic on values published by sleep-medicine bodies. They do not diagnose or treat anything. If you have symptoms — loud snoring with pauses, gasping, daytime sleepiness despite enough time in bed — see a clinician.
How the pages are built
Static HTML, one stylesheet and one script, served from this domain. No framework, no CDN, no analytics script, no cookie. The arithmetic is in the script, so the calculators work offline once loaded. A single build script generates every page, which keeps the published rules and the code that applies them in one place.
Corrections
If a number is wrong — a cycle length, an age band, a worked example — the fix belongs in the table that generates it, not in the page text. The worked examples on each page are computed from those same constants and re-checked when one changes.