The Insomnia Severity Index (ISI), Explained

What the Insomnia Severity Index is

The Insomnia Severity Index (ISI) is a brief self-report questionnaire that captures a person's own perception of how severe their insomnia is. It was developed by the sleep researcher Charles Morin and colleagues and has become one of the most widely used insomnia measures in both clinics and research, partly because it is short, is filled in by the patient rather than requiring a sleep lab, and is sensitive to change over time. It has been formally validated as a screening and outcome measure 1Ref 1Bastien CH, Vallieres A, Morin CM (2001).Validation of the Insomnia Severity Index as an outcome measure for insomnia research.That the ISI is a validated self-report instrument for screening and measuring insomnia severity..

At the level of what it measures, the ISI captures three related things: the severity of the night-time difficulty itself, whether that is trouble falling asleep, trouble staying asleep, or waking too early; how dissatisfied you are with your current sleep; and how much the problem spills into your waking life as daytime impairment and distress. Rolling those together into a single score is the point, because insomnia is not just a count of minutes spent awake. It is the whole experience of struggling with sleep and paying for it during the day.

The reference period is the last two weeks, which is short enough to reflect how you are now and long enough to smooth over one unusually good or bad night. That combination is why the same instrument can work both as a quick screen and as a way to follow someone through treatment.

How the ISI is scored

The ISI is a short questionnaire, and its scoring is deliberately simple. It contains seven items, each rated on a five-point scale from 0 to 4, and the ratings are summed into a single total that runs from 0 to 28. A higher total means more severe insomnia. Everything is anchored to the past two weeks, and the whole thing takes only a couple of minutes to complete.

What the score reflects is your perception, and that is a design choice rather than a weakness. The ISI does not measure brain waves or breathing; it measures how bad the problem feels and how much it is costing you, because insomnia is defined in part by dissatisfaction and daytime distress rather than by any single objective threshold. Two people can lose a similar amount of sleep and land at very different scores, and that difference is itself clinically meaningful. A number that captures the lived severity of the problem is exactly what a clinician wants when the complaint is, at bottom, about suffering and function rather than about a lab reading.

What the score means

The total maps onto standard severity bands, which is how a raw number becomes an interpretation. The commonly used bands place 0 to 7 in the range considered free of clinically significant insomnia, 8 to 14 as subthreshold insomnia, 15 to 21 as moderate insomnia, and 22 to 28 as severe insomnia 2Ref 2Morin CM, Belleville G, Belanger L, Ivers H (2011).The Insomnia Severity Index: psychometric indicators to detect insomnia cases and evaluate treatment response.The standard ISI severity bands, the community case-detection cutoff of about 10 (roughly 86 percent sensitivity, 88 percent specificity), and that a change of several points is a clinically meaningful improvement..

There is also a lower threshold used for case-finding. In a community sample, a total score of about 10 was the best cutoff for detecting insomnia cases, with roughly 86 percent sensitivity and 88 percent specificity 2Ref 2Morin CM, Belleville G, Belanger L, Ivers H (2011).The Insomnia Severity Index: psychometric indicators to detect insomnia cases and evaluate treatment response.The standard ISI severity bands, the community case-detection cutoff of about 10 (roughly 86 percent sensitivity, 88 percent specificity), and that a change of several points is a clinically meaningful improvement.. That is why a score in the low teens, which still sits inside the subthreshold band, can be enough to prompt a closer look: the band tells you how severe the problem is, and the cutoff tells you how likely it is that a genuine insomnia disorder is present. The ISI measures how severe insomnia is; it does not, by itself, make the diagnosis. Both the bands and the cutoff are tools for a conversation, not automatic labels.

A screen is not a diagnosis

A high ISI score means insomnia is likely, not that it has been diagnosed. The two ideas are easy to blur, but the difference matters. A questionnaire is a screen: it flags who probably has a problem and how severe it feels. A diagnosis is a clinical judgment that takes in the whole picture. Chronic insomnia disorder means trouble falling or staying asleep despite an adequate opportunity to sleep, occurring at least three nights a week for three months or more, with daytime consequences, and not better explained by another condition 3Ref 3National Heart, Lung, and Blood Institute (2022).Insomnia — What Is Insomnia?.The definition of insomnia and the three-nights-a-week-for-three-months threshold that distinguishes chronic insomnia disorder from a screening score..

The ISI cannot do several of those things. It cannot confirm you had a fair chance to sleep, it cannot rule out sleep apnea, restless legs, a medication effect, or a body-clock mismatch, and it says nothing about why the insomnia started, which is what a framework like the 3P model is for. Those are jobs for a clinician taking a history 4Ref 4Winkelman JW (2021).In the Clinic: Insomnia.The general clinical framing that diagnosis requires history and evaluation rather than a screening instrument alone, and that questionnaires are one part of assessment.. This is why a score is best understood as the opening of a conversation rather than its conclusion. It earns the problem a proper look; it does not settle what the problem is.

Understanding that boundary also protects you from two opposite mistakes: dismissing a real problem because the number felt low over a good fortnight, and panicking over a high number that turns out to have a specific, treatable cause a clinician can find.

Where to find the official ISI

The ISI is copyrighted, and that shapes where you should get it. The instrument is owned by its developers and licensed through the Mapi Research Trust and its eProvide platform, which handles permissions for clinicians and researchers. In practice it is usually administered and scored by a clinician, who can then set the result in the context of your history rather than leaving you to interpret a number on your own.

Because of the copyright, this page describes what the ISI measures and how its scores are read, but it does not reproduce the questionnaire or its wording. That is a deliberate choice, and it protects you as much as it protects the copyright holder. Small changes to how a validated item is worded can change how people answer it, so a paraphrased or pirated copy floating around online is both a legal problem and a worse measurement than the real thing. If you want to complete the official version, the reliable route is through a clinician or the official licensing source, not a screenshot from a forum or an app that copied it without permission.

How clinicians use the ISI over time

The ISI earns most of its value as a repeated measure. Given once, it is a snapshot of severity. Given at the start of care and then again as treatment goes on, it turns a vague sense of doing better or worse into a tracked line, and a drop of several points is generally read as a genuine, clinically meaningful improvement rather than one good week 2Ref 2Morin CM, Belleville G, Belanger L, Ivers H (2011).The Insomnia Severity Index: psychometric indicators to detect insomnia cases and evaluate treatment response.The standard ISI severity bands, the community case-detection cutoff of about 10 (roughly 86 percent sensitivity, 88 percent specificity), and that a change of several points is a clinically meaningful improvement.. That is precisely the property that makes it the standard outcome measure in insomnia research.

It is also how the field knows its treatments work. The behavioral treatments for chronic insomnia have been evaluated largely by watching scores like the ISI fall, and the pooled evidence behind them has been formally graded 5Ref 5Edinger JD, Arnedt JT, Bertisch SM, et al. (2021).Behavioral and psychological treatments for chronic insomnia disorder in adults: an American Academy of Sleep Medicine systematic review, meta-analysis, and GRADE assessment.That behavioral treatments for chronic insomnia are supported by formally graded evidence, evaluated using insomnia-severity outcome measures.. Even brief, sleep-focused interventions delivered in ordinary general practice have been shown to lower insomnia-severity scores compared with basic advice 6Ref 6Falloon K, Elley CR, Fernando A 3rd, Lee AC, Arroll B (2015).Simplified sleep restriction for insomnia in general practice: a randomised controlled trial.That a brief sleep-focused intervention in general practice lowered insomnia-severity scores compared with basic sleep advice.. When those treatments are packaged as digital CBT-I and delivered through an app or website, the same score is what tells you whether the program is actually helping. The number is not the goal of treatment, but it is how both you and your clinician can see, honestly and over time, whether the goal is being reached.

Common ways an ISI score gets misread

A few predictable misreadings turn a useful number into a source of unnecessary worry or false reassurance. The first is treating the total as a diagnosis, which it is not: a score of 17 does not mean you have been diagnosed with anything, only that your insomnia is registering as moderate right now. The second is over-reading a single administration. Because the window is two weeks, a rough fortnight can push the score up and a calm one can pull it down, so the trend across repeated measures is more trustworthy than any one result.

A third misreading is assuming the score reflects how much sleep you objectively lost. It does not; it reflects severity and distress, which is why someone can score high on relatively little measured sleep loss, and why the number is meaningful even when a sleep study looks unremarkable. A fourth is treating a low score during treatment as permission to abruptly abandon the habits that produced it, when holding the gains is its own task. Read the way it was designed, as a tracked and openly subjective severity gauge rather than a verdict, the ISI is genuinely useful and hard to misuse.

How the ISI compares with other sleep questionnaires

The ISI is not the only sleep questionnaire, and it is built for a particular job: gauging insomnia severity quickly and tracking it. Other tools answer different questions. The Pittsburgh Sleep Quality Index (PSQI) casts a wider net over overall sleep quality across several components, which makes it useful for a broad picture but less sharply focused on insomnia severity. The Athens Insomnia Scale is another brief insomnia questionnaire, built closely around diagnostic criteria, that a clinician might reach for instead.

None of these is a diagnosis, and none replaces the others; they are instruments, and a clinician picks the one that fits what needs measuring. Daytime sleepiness scales, which ask how likely you are to doze off during ordinary activities, measure something different again and are more relevant to conditions like sleep apnea than to insomnia.

If you already have a number in hand, the most useful next step is not to compare instruments but to understand your own result. Reading your insomnia severity score in context, against the bands and the case-finding cutoff, tells you far more than knowing which questionnaire produced it.