Insomnia Severity Index Calculator

Introduction: Understanding the Insomnia Severity Index (ISI)

The Insomnia Severity Index (ISI) is a seven-item self-report questionnaire that summarizes the severity of insomnia symptoms and their daytime consequences. Rather than measuring sleep with a device, the ISI records how you have experienced trouble sleeping, dissatisfaction with sleep, impairment, and distress.

ISI responses are usually considered over the past two weeks. Use your typical experience during that period for every item so that the resulting score describes one consistent window of sleep difficulty.

For an ISI score to be useful, answer each sleep question from your own recent experience rather than from what you think a “good sleeper” should report. The first three items distinguish difficulty getting to sleep, difficulty remaining asleep, and waking earlier than intended; they are related but not interchangeable experiences. The remaining items capture satisfaction and the perceived daytime or emotional impact of the sleep problem. A person can have a short sleep period without rating every ISI item highly, while another person may have considerable worry, dissatisfaction, or functional interference even when the amount of sleep varies from night to night.

The ISI is best read as a concise snapshot of perceived insomnia burden. It does not require estimating exact hours slept, counting awakenings, or calculating sleep efficiency. If your sleep schedule has recently changed because of travel, shift work, illness, caregiving, or a new medication, keep that context in mind when comparing this score with a later ISI result.

How the ISI score is calculated

This Insomnia Severity Index calculator assigns the selected value from 0 to 4 to each of the seven ISI items, with higher values representing greater symptoms or impact. It then adds those values, producing a total from 0 to 28.

Insomnia Severity Index scoring formula

For the ISI scoring formula, the seven response values are added without weighting:

Total ISI = Q1 + Q2 + Q3 + Q4 + Q5 + Q6 + Q7

In MathML form:

Here, S_i is the 0–4 response selected for ISI item i.

Interpreting your ISI results

An Insomnia Severity Index total is commonly grouped into the following score ranges:

• 0–7: No clinically significant insomnia
• 8–14: Subthreshold insomnia
• 15–21: Moderate insomnia
• 22–28: Severe insomnia

These ISI categories are a screening and monitoring aid, not a diagnosis. They can help frame a conversation about sleep care or show whether symptoms are changing, particularly when poor sleep is affecting daytime functioning.

An ISI category should not be treated as a complete explanation for why sleep is difficult. The same total can result from different response patterns: one person may primarily report problems falling asleep, whereas another may report less trouble at night but high dissatisfaction and daytime interference. Looking back at the individual answers can make the total more informative and can help identify which aspect of sleep feels most disruptive. When repeating the questionnaire, use the same two-week perspective and compare both the total and the pattern of responses. A small change in score may reflect a meaningful change in one troublesome area, while a stable total can sometimes conceal improvement in one item and worsening in another.

ISI score ranges and practical context

This ISI score range table connects each total with the kind of follow-up that may be useful while keeping the result in its clinical context.

Worked example: adding seven ISI item scores

This Insomnia Severity Index example shows how individual sleep-related ratings become one total score:

• 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.

An ISI score of 16 is in the 15–21 range, commonly described as moderate insomnia. The total does not establish a diagnosis, but it indicates that the reported sleep problem and its effects are substantial enough to consider a structured response, such as CBT-I, and clinical discussion when symptoms persist.

ISI limitations and assumptions

The Insomnia Severity Index is useful for describing perceived insomnia burden, but its score has important limits:

• 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, such as stress, circadian rhythm issues, sleep apnea, or medication effects.
• Comorbid conditions: Depression, anxiety, chronic pain, substance use, shift work, and other factors can strongly influence ISI responses and may require targeted support.
• Doesn’t measure objective sleep: The ISI does not directly measure sleep duration or sleep efficiency; it complements, rather than replaces, clinical assessment or sleep testing when indicated.
• Urgent symptoms: If severe daytime sleepiness makes driving unsafe, you have breathing pauses or gasping at night, or you have thoughts of self-harm, seek urgent medical help rather than relying on an ISI score.

Because the ISI is based on ratings, it is not designed to determine whether a particular sleep treatment is appropriate or to separate insomnia from every other sleep or health condition. Use the result as one piece of information. Persistent sleep difficulty, a rapidly worsening pattern, or concerns about safety deserve attention even if a single questionnaire result does not seem to capture every detail.

How to use: Using the ISI to track change over time

The Insomnia Severity Index is particularly useful for following change in perceived sleep difficulty over time. When trying sleep-schedule changes, stimulus control, or CBT-I, retake the ISI at consistent intervals, such as every 2–4 weeks, and compare totals instead of giving undue weight to a single night.

For consistent ISI tracking, complete all seven items at roughly the same point in your routine and think back over the same recent period each time. Record any major circumstances that may have affected sleep, such as an acute illness, unusual work hours, or a stressful event. This context can help you interpret a higher or lower score without assuming that every movement represents a lasting change in insomnia severity.

Attribution for the Insomnia Severity Index

The Insomnia Severity Index is a widely used instrument developed and validated in clinical research, commonly attributed to Charles M. Morin and colleagues. For healthcare decisions, consider reviewing ISI responses with a qualified clinician who can interpret the score alongside your symptoms and circumstances.