Expand the sleep window by fifteen minutes when efficiency improves

Once sleep efficiency exceeds 85–90% for a week, add fifteen minutes to the window — then repeat.

Why it works

Sleep restriction is not a permanent state; it is a catalyst that rebuilds sleep quality, then gets titrated upward as the efficiency improves. Expanding the window by fifteen minutes per week when efficiency stays above the threshold gradually returns the person to adequate total sleep while maintaining the efficiency gains. Moving too fast expands the window before the efficiency is stable, reintroducing fragmentation.

How to do it

1. At the end of each week, calculate sleep efficiency from your logs.
2. If efficiency is 85% or above for five of seven nights, add fifteen minutes to the sleep window (usually by moving bedtime fifteen minutes earlier).
3. If efficiency is below 85%, hold the current window or reduce by fifteen minutes and wait another week.

Evidence

The 85–90% efficiency threshold for window expansion is the standard Spielman titration criterion; the gradual titration approach is the established CBT-I clinical protocol. (clinical)

The 85% threshold is a clinical heuristic; some protocols use different thresholds. The key principle is that efficiency must be stable before expanding the window.

Sources

• Spielman, Saskin & Thorpy (1987), treatment of chronic insomnia by restriction of time in bed, Sleep

Common mistake

Adding more time to the window the first time you have a good night rather than waiting for a full week of consistent data — one good night is noise; a week of 85%+ efficiency is signal.