Insomnia Severity Index: Score Your Sleep

What Is the Insomnia Severity Index?

The Insomnia Severity Index (ISI) is a brief, validated questionnaire that measures how severe your insomnia is and how much it affects your daily life. It was developed by Charles Morin and colleagues at Laval University and published by Bastien, Vallieres, and Morin in 2001 in Sleep Medicine. The original validation study demonstrated strong internal consistency (Cronbach's alpha = 0.74) and sensitivity to treatment-related changes in insomnia symptoms.

The ISI asks seven questions, each rated 0 to 4, producing a total score from 0 to 28. It covers three core dimensions: the severity of your sleep difficulties (falling asleep, staying asleep, waking too early), your satisfaction with your current sleep, and the degree to which insomnia interferes with your daily functioning.

Sleep specialists use the ISI both as a screening tool and as an outcome measure. It is short enough to administer at every clinical visit, making it ideal for tracking whether a treatment is actually working. The Canadian Sleep Society, the American Academy of Sleep Medicine, and the European Sleep Research Society all recognize it as a standard instrument for insomnia assessment.

If you have been struggling with your sleep and want a structured way to gauge the severity, take the Insomnia Severity Index now.

How the ISI Is Scored

Each of the seven questions is scored from 0 (no problem) to 4 (very severe problem). The total score ranges from 0 to 28 and maps to four clinical categories:

• 0 to 7: No clinically significant insomnia
• 8 to 14: Subthreshold insomnia (below clinical thresholds, but symptoms present)
• 15 to 21: Moderate clinical insomnia
• 22 to 28: Severe clinical insomnia

These cutoff values were established in the original 2001 validation study and have been confirmed in subsequent research. A 2011 study by Morin, Belleville, Belanger, and Ivers in Sleep validated the cutoff of 10 as optimal for detecting insomnia cases in community samples (sensitivity 97.2%, specificity 100%), while the clinical cutoffs of 15 and 22 effectively distinguish moderate from severe cases.

The ISI is designed to be interpreted alongside clinical context, not as a standalone diagnosis. A score of 16 from someone who has always been a light sleeper means something different than a 16 from someone whose sleep collapsed after starting a new medication.

Why Insomnia Matters for CPAP Users

If you use a CPAP machine, insomnia is not a separate problem you can ignore. Research shows that 30 to 50% of people diagnosed with obstructive sleep apnea (OSA) also have clinically significant insomnia, a condition researchers call COMISA (Co-Morbid Insomnia and Sleep Apnea). Wickwire et al. published a comprehensive review in Chest (2019) documenting this overlap and its consequences.

COMISA is more than an inconvenience. People with both conditions have worse outcomes than those with either one alone. They are less likely to adhere to CPAP therapy, report more daytime fatigue despite treatment, and have higher rates of depression and cardiovascular risk (Sweetman et al., 2017, Sleep Medicine Reviews).

The practical implication: if your CPAP data shows your AHI is well controlled but you still feel terrible during the day, insomnia may be the missing piece. CPAP treats the airway obstruction. It does not treat the racing thoughts, hyperarousal, or conditioned wakefulness that drive insomnia. Both problems need their own interventions.

Check your ISI score to see where you stand, then use CPAP Clarity's data analyzer to review whether your therapy is addressing the apnea side of the equation.

What Each Severity Level Means

No Clinically Significant Insomnia (0 to 7)

A score in this range suggests your sleep difficulties, if any, are within normal limits. Everyone has occasional bad nights, and a score of 3 or 5 does not mean you have a sleep disorder. If you are sleeping reasonably well most of the time and functioning during the day, no clinical intervention is needed.

That said, maintaining good sleep habits is worthwhile at any score. Consistent bedtimes, limited screen exposure before bed, and a cool, dark sleep environment all help prevent insomnia from developing. Research by Chang et al. (2015, PNAS) showed that reading on a light-emitting device before bed delayed melatonin onset by 1.5 hours and reduced next-morning alertness compared to reading a printed book. Simple environment changes, like keeping your bedroom at 60 to 67 degrees Fahrenheit and removing screens an hour before bed, are among the most effective preventive measures. Use the Sleep Cycle Calculator to find the bedtime that aligns with your natural sleep cycles.

Subthreshold Insomnia (8 to 14)

This range indicates early or mild insomnia symptoms. You are noticing sleep difficulties, but they may not yet be severe enough to significantly impair your daytime functioning. This is the stage where behavioral changes have the highest chance of preventing escalation.

The most effective behavioral strategies at this stage include stimulus control (only go to bed when sleepy, get up if you cannot sleep within 20 minutes), sleep restriction (limit time in bed to match actual sleep time), and cognitive restructuring (addressing worry and catastrophizing about sleep). These techniques are components of Cognitive Behavioral Therapy for Insomnia (CBT-I).

A white noise machine (opens in new tab) can help mask environmental noise that fragments light sleep. A weighted blanket (opens in new tab) may reduce anxiety and improve perceived sleep quality, based on findings by Ekholm et al. (2020) in the Journal of Clinical Sleep Medicine.

Moderate Clinical Insomnia (15 to 21)

At this level, insomnia is clearly affecting your quality of life. You are likely experiencing difficulty with concentration, mood, energy, or relationships as a direct result of poor sleep. This score warrants professional attention.

CBT-I is the recommended first-line treatment for chronic insomnia at this severity. The American College of Physicians issued a strong recommendation for CBT-I over medication as initial therapy (Qaseem et al., 2016, Annals of Internal Medicine). A meta-analysis by Trauer et al. (2015, Annals of Internal Medicine) found that CBT-I improved sleep onset latency by 19 minutes, wake after sleep onset by 26 minutes, and sleep efficiency by 9.9 percentage points, with effects maintained at follow-up.

CBT-I programs are available through trained therapists, online platforms, and some primary care settings. If access is a barrier, digital CBT-I programs have been shown to produce similar effect sizes in randomized trials (Espie et al., 2012, JAMA Psychiatry).

If you are a CPAP user with a moderate ISI score, it is especially important to examine whether both conditions are being addressed. Use CPAP Clarity to track your therapy data and bring both your CPAP report and ISI score to your next sleep appointment. Physicians find it helpful when patients quantify both sides of the problem.

Severe Clinical Insomnia (22 to 28)

A score in this range indicates insomnia that is severely impairing your daily life. Professional evaluation is strongly recommended. Severe insomnia is associated with increased risk for depression, anxiety, substance use, and impaired occupational functioning.

Treatment typically combines CBT-I with pharmacological options under medical supervision. Your healthcare provider may also investigate contributing factors such as medications, pain conditions, mood disorders, or untreated sleep apnea. If you have not been evaluated for sleep apnea, the STOP-BANG Screener or the Berlin Questionnaire can help you assess that risk.

Optimizing your sleep environment matters at every severity level but becomes critical here. Blackout curtains (opens in new tab) eliminate light intrusion that can prevent melatonin onset. A cool room temperature (60 to 67 degrees Fahrenheit) supports your body's natural temperature drop during sleep initiation.

How Often Should You Retake the ISI?

The ISI is designed to be repeated. Morin et al. (2011) recommend retaking it at regular intervals to track treatment response. A change of 6 or more points is considered a clinically meaningful difference, and a post-treatment score below 8 indicates remission.

Tracking your score over time is especially valuable if you are making lifestyle changes or starting a new treatment. A single score is a snapshot. A trend line across multiple assessments shows whether your interventions are working, plateauing, or losing effectiveness. Many CBT-I programs incorporate the ISI at every session for exactly this reason.

If you are in CBT-I treatment, taking the ISI every two weeks gives you and your provider a clear trend line. If you are managing on your own with behavioral strategies, monthly check-ins are a reasonable cadence. Retake the ISI any time to see how your score has changed.

How the ISI Compares to Other Screening Tools

The ISI is specifically designed for insomnia. It does not screen for sleep apnea, restless legs, circadian rhythm disorders, or other sleep conditions. If you suspect you might have multiple sleep problems, consider pairing it with:

• Epworth Sleepiness Scale: Measures daytime sleepiness, which can indicate untreated sleep apnea or other hypersomnia causes
• STOP-BANG Screener: Estimates your risk of obstructive sleep apnea
• Berlin Questionnaire: Assesses sleep apnea risk across snoring, sleepiness, and BMI categories

No single screening tool captures the full picture. Using two or three together gives you and your provider much more to work with than any one score alone.

The Research Behind the ISI

The ISI has been validated in multiple populations and languages. Key studies include:

• Bastien, Vallieres, Morin (2001) in Sleep Medicine: Original validation demonstrating internal consistency and clinical sensitivity across insomnia severity groups
• Morin, Belleville, Belanger, Ivers (2011) in Sleep: Large-scale validation (n=1,670) establishing optimal cutoff scores for community and clinical populations
• Sierra, Guillen-Serrano, Santos-Iglesias (2008) in Sleep Medicine: Spanish validation confirming the single-factor structure across cultural contexts
• Gagnon et al. (2013) in Sleep Medicine: Demonstrated the ISI's ability to detect clinically meaningful change in response to CBT-I treatment

The ISI is freely available for clinical and research use, which has contributed to its widespread adoption. It is one of the most cited insomnia instruments in the peer-reviewed literature.

Take the ISI Now

Ready to see where you stand? The Insomnia Severity Index takes about two minutes. Your answers stay on your device, nothing is sent to a server, and you can retake it any time to track changes.

If your score suggests moderate or severe insomnia, bring it to your next healthcare appointment. Quantified sleep complaints are easier for providers to act on than vague descriptions of "not sleeping well."

For CPAP users, combining your ISI score with your CPAP therapy data gives the most complete picture of your sleep health. Treat the apnea, address the insomnia, and track both over time.

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