Insomnia Severity Index (ISI)

A concise 7-item clinical instrument designed to evaluate the nature, severity, and daytime impact of insomnia symptoms.

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Question 1 of 70 / 7 (0%)

Difficulty falling asleep (How much difficulty do you have falling asleep?)

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How it is calculated

7 questions rated from 0 to 4 points. Total score ranges from 0 to 28, covering sleep onset, sleep maintenance, early morning awakenings, and daytime impairment.

Formula

Total ISI Score = Sum of all 7 items (0–28). 0–7: No clinically significant insomnia; 8–14: Subthreshold (mild); 15–21: Clinical insomnia (moderate); 22–28: Severe clinical insomnia.

Limits of the method

This index is intended for screening. If obstructive sleep apnea, restless legs syndrome, or chronic parasomnia is suspected, polysomnography is required.

Sources of the method

This calculation is for reference only and is not medical advice, a diagnosis or a prescription. If you have a medical condition, are pregnant, take medication or have any doubts, discuss the result with a physician or a qualified nutrition professional.

How to Complete the ISI Questionnaire

Reflect on the past 2 weeks

Evaluate how you have been sleeping and how rested you have felt during the day over the last 14 days.

Answer all 7 questions

Rate the severity of each issue from 0 ('None') to 4 ('Very severe').

Review your score and sleep recommendations

Check your severity category and implement targeted sleep hygiene strategies.

Representative ISI Profiles

Normal4 points

Restorative Healthy Sleep

Quick sleep onset, stable nocturnal sleep architecture, and waking refreshed.

Maintain consistent sleep-wake schedules and appropriate circadian light exposure.

Subthreshold11 points

Mild Subclinical Insomnia

Occasional difficulty falling asleep, light sleep, and mild afternoon fatigue.

Optimize bedroom environment (cool, dark, quiet) and reduce evening caffeine and screens.

Clinical19 points

Moderate to Severe Clinical Insomnia

Frequent nocturnal awakenings, premature morning waking, daytime exhaustion, and anxiety around bedtime.

Consultation with a somnologist or behavioral sleep medicine specialist is indicated.

Adenosine, Melatonin, and the Two-Process Sleep Model

Sleep regulation relies on Borbély's Two-Process Model: Process S (homeostatic sleep drive powered by adenosine accumulation) and Process C (circadian rhythm driven by the suprachiasmatic nucleus).

Stimulus Control and Cognitive Restructuring in CBT-I

Strengthening the mental association between bed and sleep while breaking conditioned bedroom anxiety is the foundational pillar of non-pharmacological insomnia recovery.

ISI Severity Cutoff Scores

ISI Score	Insomnia Severity	Recommended Strategy
0 – 7	No Clinically Significant Insomnia	Normal sleep quality; preserve healthy circadian habits
8 – 14	Subthreshold Insomnia	Sleep hygiene optimization, stress reduction, caffeine curfew
15 – 21	Moderate Clinical Insomnia	CBT-I structured therapy, sleep restriction, stimulus control
22 – 28	Severe Clinical Insomnia	Somnological and psychiatric medical consultation

Validated by C.M. Morin et al. (2001). Recognized internationally as the primary standard in sleep medicine.

Frequently asked questions

What does my ISI score mean?

The score reflects the overall clinical severity of sleep disturbances and their daytime psychological and physical consequences over recent weeks.

What sleep latency is considered physiologically normal?

Falling asleep within 10 to 20 minutes is considered optimal. Falling asleep in under 5 minutes indicates severe sleep deprivation; taking over 30 minutes signals insomnia.

What should I do if I wake up in the middle of the night and cannot fall back asleep?

Apply stimulus control therapy: if unable to sleep after ~20 minutes, get out of bed, move to a dimly lit room, engage in quiet reading, and return to bed only when sleepy.

How do blue screens impact nighttime sleep?

Blue light (460–480 nm) emitted by screens suppresses pineal melatonin secretion, delaying circadian phase and increasing sleep onset latency.

Is taking sleeping pills recommended as a first-line solution?

No. International clinical guidelines establish CBT-I as the gold standard first-line treatment, as medications carry risks of tolerance and rebound insomnia.

Calculate your optimal wake-up times with the Sleep Cycles calculator and assess stress with the PSS-10.

Sleep Cycles Calculator →Perceived Stress Scale (PSS-10) →Patient Health Questionnaire-9 (PHQ-9 Depression) →Caffeine Clearance & Sleep Timing Calculator →

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What next

Formula breakdowns, biomarker reference ranges and nutrition articles with cited sources are in the NutriFit knowledge base.

Go to the knowledge base