Deep Sleep Duration
Deep Sleep Duration is the cumulative time spent in slow-wave sleep (N3) during a sleep period. In research contexts, this stage is also called delta sleep or slow-wave sleep (SWS), characterized by high-amplitude, low-frequency brain waves. Deep sleep differs from light sleep (N1, N2) and REM sleep in its distinct electrophysiological signature and associated functions. The metric captures time in this specific stage; it does not assess the quality or continuity of deep sleep episodes.
Typical Adult Ranges
% of total sleepBased on population studies. Individual needs vary by age and health status.
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Key Takeaways
Represents time spent in slow-wave sleep (N3 stage).
Concentrates in the first half of the night.
Associated with physical restoration and growth hormone release.
Declines with age; personal baseline reflects individual physiology.
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How It's Measured
Oura estimates Deep Sleep Duration by classifying sleep epochs based on heart rate, heart rate variability, movement, and respiratory patterns.
Common Influences
Prior wakefulness: Longer time awake before sleep is associated with increased slow-wave activity and deep sleep duration (homeostatic sleep drive).
Deep Dive
Deep Sleep Duration represents the quantity of time spent in the most physically restorative sleep stage. It reflects the portion of the night when slow-wave activity dominates, growth hormone secretion peaks, and metabolic recovery processes are most active.
A useful framing is that deep sleep represents the foundation of physical restoration. The duration indicates how much time was spent in this state; it does not guarantee that restorative processes completed successfully. Deep sleep is necessary but not sufficient for feeling physically recovered.
Deep sleep is characterized by synchronized, slow-frequency brain oscillations (0.5β4 Hz delta waves). During this stage, parasympathetic activity increases, heart rate and blood pressure reach their lowest levels, and growth hormone is released in pulses. Tissue repair, immune function support, and metabolic waste clearance are associated with this stage.
Deep sleep concentrates in the first half of the night, with the longest episodes occurring in early sleep cycles. Later cycles typically contain less deep sleep and more REM sleep. This architecture means that delayed bedtimes or early awakenings may disproportionately affect different sleep stages.