Insomnia Severity Index Calculator
Understanding the Insomnia Severity Index (ISI)
The Insomnia Severity Index (ISI) is a 7-item, self-report questionnaire used in clinical and research settings to quickly summarize how severe your insomnia symptoms feel and how much they affect daytime life. It focuses on your perceived sleep difficulty (not device-measured sleep) and on how disruptive those difficulties are.
Most versions of the ISI ask you to rate symptoms over the past two weeks. For the most consistent and comparable results, answer each question based on your typical experience during that period.
How the ISI score is calculated
Each of the 7 questions is scored from 0 to 4 (where higher numbers reflect more severe symptoms or impact). Your total ISI score is the sum of all item scores, so totals range from 0 to 28.
Formula
In plain terms:
Total ISI = Q1 + Q2 + Q3 + Q4 + Q5 + Q6 + Q7
In MathML form:
Where Si is the score (0–4) you selected for each item.
Interpreting your ISI results
Your total score is commonly interpreted using these ranges:
- 0–7: No clinically significant insomnia
- 8–14: Subthreshold insomnia
- 15–21: Moderate insomnia
- 22–28: Severe insomnia
These bands are a screening/monitoring aid. They can help you decide whether to try structured self-care (sleep hygiene, stimulus control) and/or discuss symptoms with a clinician—especially when daytime functioning is affected.
Score ranges and practical context
| ISI score | Category | What it often suggests | Common next step (non-diagnostic) |
|---|---|---|---|
| 0–7 | No clinically significant insomnia | Sleep difficulties are minimal or not persistently disruptive. | Maintain healthy sleep habits; recheck if symptoms change. |
| 8–14 | Subthreshold insomnia | Noticeable symptoms, but impact may be intermittent or mild. | Consider sleep hygiene and tracking patterns for 2–4 weeks. |
| 15–21 | Moderate insomnia | More frequent symptoms and/or meaningful daytime impairment. | Consider structured approaches like CBT-I; discuss with a clinician if persistent. |
| 22–28 | Severe insomnia | High symptom burden and significant distress/impairment. | Strongly consider professional evaluation; ask about CBT-I and underlying contributors. |
Worked example
Suppose you answer the 7 items with the following scores:
- Q1 (falling asleep): 3
- Q2 (staying asleep): 2
- Q3 (waking too early): 2
- Q4 (sleep satisfaction): 3
- Q5 (interference with daily functioning): 2
- Q6 (noticeable impairment): 1
- Q7 (distress): 3
Total ISI = 3 + 2 + 2 + 3 + 2 + 1 + 3 = 16.
A score of 16 falls in the 15–21 band, typically labeled moderate insomnia. That doesn’t diagnose a condition by itself, but it does suggest your sleep difficulty and its impact are substantial enough that a structured plan (often CBT-I) may be worthwhile.
Limitations and assumptions (important)
- Self-report and subjectivity: The ISI captures how you perceive your sleep and its impact. Two people with similar sleep duration may score differently.
- Typical timeframe: The ISI is generally interpreted as reflecting the past two weeks. If you answer based on a single unusually bad (or good) night, the result may be misleading.
- Not a diagnosis: ISI scores are informational. They do not confirm insomnia disorder or identify the cause (e.g., stress, circadian rhythm issues, sleep apnea, medication effects).
- Comorbid conditions: Depression, anxiety, chronic pain, substance use, shift work, and other factors can strongly influence scores and may require targeted support.
- Doesn’t measure objective sleep: The tool does not directly measure sleep duration/efficiency; it complements (but doesn’t replace) clinical assessment or sleep testing when indicated.
- Urgent symptoms: If you have severe daytime sleepiness that makes driving unsafe, breathing pauses/gasping at night, or thoughts of self-harm, seek urgent medical help rather than relying on a questionnaire score.
Using the ISI to track change over time
The ISI can be helpful for monitoring trends. If you’re trying an intervention (sleep schedule changes, stimulus control, CBT-I), consider re-taking the ISI at consistent intervals (for example, every 2–4 weeks) and comparing totals, rather than focusing on day-to-day fluctuations.
Attribution
The ISI is a widely used instrument developed and validated in clinical research (commonly attributed to Charles M. Morin and colleagues). If you are using this tool for healthcare decisions, consider completing it with a qualified clinician who can interpret it in context.