Sleep restriction therapy starts with one number: your sleep window — how long you are allowed to spend in bed. Get it from your sleep diary, anchor it to a fixed wake-up time, and adjust it weekly from your sleep efficiency.
This calculator does the arithmetic for you.
Sleep restriction calculator
Enter your average sleep time from 1–2 weeks of sleep diary entries and the wake-up time you can hold every day. The calculator returns a starting sleep window and the bedtime it implies — the schedule sleep restriction therapy begins from.
Your diary baseline
Average actual sleep — not time in bed.
Earliest bedtime 00:45, fixed wake-up 07:00. Go to bed no earlier than this — later is fine if you are not sleepy yet.
- ≥ 90% sleep efficiency → widen the window by 15–30 min
- 85–89% → keep the window for another week
- < 85% → keep or narrow by 15 min (never below 5 h 30 min)
Educational estimate, not a prescription. Review the safety section below before starting, and adjust from weekly diary averages — not single nights.
How the calculator works
The method comes from the original Spielman sleep restriction protocol, which is still the core of how CBT-I programs set sleep windows today:
- Average sleep time, not time in bed. Take 1–2 weeks of sleep diary entries and average how long you actually slept each night. If you spend 8 hours in bed but sleep 6 h 15 min, your baseline is 6 h 15 min.
- The window matches your average sleep. Your initial time in bed is set to that average — with a safety floor of 5 h 30 min. Clinical programs do not restrict below that even when diary averages are lower.
- The wake-up time is the anchor. You pick one wake-up time you can hold every day, including weekends. The calculator derives your earliest bedtime backwards from it.
The result feels strict on purpose: by matching time in bed to actual sleep, you concentrate sleep pressure so the night becomes more solid and predictable.
The weekly adjustment rules
The window is not fixed forever. Once a week, compute your average sleep efficiency across the diary week and adjust:
| Weekly sleep efficiency | Adjustment |
|---|---|
| 90% or higher | Widen the window by 15–30 minutes |
| 85–89% | Keep the window unchanged for another week |
| Below 85% | Keep it, or narrow by 15 minutes (never below 5 h 30 min) |
Two practical rules make or break the process:
- Adjust weekly, not nightly. One rough night is data, not a verdict.
- Move the bedtime, not the wake-up. The wake-up anchor is what stabilizes your body clock.
What to expect in the first weeks
The first 1–2 weeks usually involve more daytime sleepiness — that is the sleep pressure building. Most structured programs see sleep consolidate first (fewer long awakenings), then the window gradually expands toward your real sleep need. The full mechanism, evidence, and step-by-step protocol are in our guide to sleep restriction therapy.
Safety: who should not do this alone
This page is educational, not a prescription. Do not run sleep restriction on your own if any of these apply — involve a qualified clinician instead:
- a safety-sensitive job (driving, machinery, healthcare night shifts);
- untreated or suspected sleep apnea;
- seizure risk or epilepsy;
- bipolar disorder or any history of mania (sleep loss can trigger episodes);
- pregnancy;
- severe daytime sleepiness already present.
If you start and daytime sleepiness becomes unsafe, widen the window and talk to a clinician.
Why an app helps
The arithmetic is the easy part. The hard part is keeping the diary every morning, computing weekly averages honestly, and adjusting the window by the rules instead of by mood. Zomni keeps the sleep diary, tracks sleep efficiency trends, and walks you through the window adjustments week by week — so the protocol actually gets followed. If you want to compare options first, see the CBT-I app comparison.
Your Personal Sleep Coach
AI-powered insights and personalized guidance for better sleep
References
- Spielman AJ, Saskin P, Thorpy MJ. Treatment of chronic insomnia by restriction of time in bed. Sleep. 1987. PMID: 3563246
- Edinger JD, et al. Behavioral and psychological treatments for chronic insomnia disorder in adults: an American Academy of Sleep Medicine clinical practice guideline. Journal of Clinical Sleep Medicine. 2021. DOI: 10.5664/jcsm.8986
Disclaimer: Zomni is a CBT-I-informed sleep improvement app, not a medical device and not a substitute for professional medical advice. If your sleep problems may be linked to a medical, psychiatric, medication, pregnancy, or safety issue, consult a qualified clinician.
