Insomnia Severity Index (ISI): Scoring, Interpretation and Clinical Use
A 7-item self-report measure of insomnia severity, distress and daytime impact over the past two weeks.
What the ISI measures
The Insomnia Severity Index (ISI) is the most widely used brief self-report measure of insomnia. It asks about seven things: difficulty falling asleep, difficulty staying asleep, waking too early, satisfaction with sleep, how noticeable the sleep problem is to others, how distressing it is, and how much it interferes with daily functioning.
Unlike a sleep diary, which records what happened, the ISI captures how severe and how impairing the patient perceives the problem to be. That perception is what treatment for insomnia — particularly CBT-I — is designed to change, which is why the ISI is the standard outcome measure in insomnia trials.
Each item is rated 0 to 4 over the last two weeks, giving a total between 0 and 28. The measure takes two to three minutes, is sensitive to change, and can be repeated every one to two weeks during treatment without meaningful practice effects.
How to score the ISI
Score range: 0-28 (seven items, each scored 0-4)
- 1Score items 1a, 1b and 1c (falling asleep, staying asleep, waking too early) from 0 = none to 4 = very severe.
- 2Score item 2 (satisfaction with current sleep pattern) from 0 = very satisfied to 4 = very dissatisfied.
- 3Score item 3 (interference with daily functioning) from 0 = not at all to 4 = very much interfering.
- 4Score item 4 (how noticeable to others) from 0 = not at all noticeable to 4 = very much noticeable.
- 5Score item 5 (how worried or distressed) from 0 = not at all to 4 = very much worried.
- 6Add all seven item scores for a total from 0 to 28. There are no reverse-scored items and no subscales.
ISI score interpretation
| Score | Severity | What it means clinically |
|---|---|---|
| 0-7 | No clinically significant insomnia | Sleep complaints, if any, are within normal variation. No insomnia-specific treatment indicated. This is also the remission target for CBT-I. |
| 8-14 | Subthreshold insomnia | Real but mild sleep difficulty. Sleep hygiene, stimulus control and brief behavioural intervention are usually enough. Screen for a driver such as pain, alcohol, caffeine, shift work or untreated anxiety. |
| 15-21 | Moderate clinical insomnia | Clinically significant insomnia. CBT-I is first-line. Expect daytime consequences — concentration, mood, irritability. Assess for sleep apnoea and restless legs before assuming primary insomnia. |
| 22-28 | Severe clinical insomnia | Severe insomnia with marked distress and daytime impairment. Treat actively, review any hypnotic use, and consider a sleep-medicine referral if the picture does not fit behavioural insomnia. |
What specific ISI scores mean
What does an ISI score of 8 mean?
Eight is the bottom of the subthreshold range and the usual screening cut-off for detecting insomnia in a community sample. It means there is a genuine sleep complaint that is not yet clinically severe. Brief behavioural advice plus a two-week recheck is a reasonable response.
What does an ISI score of 10 mean?
Ten sits in the subthreshold band — a mild but real insomnia problem, typically with some dissatisfaction and mild daytime effect. It is above the cut-off used in most clinical samples (10 or higher), so it warrants a sleep history rather than reassurance alone.
What does an ISI score of 15 mean?
Fifteen is the threshold for moderate clinical insomnia. It usually means most nights are affected and daytime functioning is measurably worse. This is the level at which CBT-I is clearly indicated.
What does an ISI score of 22 or higher mean?
Twenty-two and above is severe insomnia. Patients at this level almost always report significant distress and daytime impairment, and frequently have a comorbid condition — depression, PTSD, chronic pain, or hypnotic dependence — that needs addressing in parallel.
How much change on the ISI is meaningful?
A reduction of about 6 points is generally treated as a clinically meaningful improvement, and a final score below 8 as remission. Change of 1-2 points is within measurement noise.
Two cut-offs, two purposes
The ISI has two commonly cited cut-offs and they are not interchangeable. A cut-off of 10 maximises detection in general or community populations. A cut-off of 15 is used in clinical settings, where you want to identify moderate-to-severe insomnia that clearly justifies treatment.
Decide which one you are using before you deploy the measure across a caseload, and keep it constant, or your prevalence numbers will drift for reasons that have nothing to do with your patients.
What the ISI does not tell you
- It does not diagnose insomnia disorder — DSM-5 requires frequency (three nights a week), duration (three months) and daytime impact, assessed clinically.
- It does not screen for sleep apnoea. A high ISI with loud snoring, witnessed apnoeas, or morning headaches needs an apnoea screen (for example the STOP-BANG), not CBT-I alone.
- It does not separate sleep-onset from sleep-maintenance insomnia in a scored way; read items 1a-1c individually for that.
- It does not capture circadian problems. A patient who sleeps well from 3am to 11am may score high because of social mismatch, not insomnia.
Using the ISI to track treatment
The ISI is the standard outcome measure across CBT-I trials, so repeated administration lets you compare your own results against published benchmarks. In well-delivered CBT-I, most responders show meaningful change by session four and remission by session six to eight.
A flat ISI after four weeks of adherent behavioural treatment is a signal to reassess: check adherence to sleep restriction, screen again for apnoea, review stimulants, alcohol and evening cannabis use, and reconsider comorbid depression or PTSD as the primary driver.
Who the ISI is for
- Adults reporting trouble falling asleep, staying asleep, or waking unrefreshed
- Patients being screened for or treated with CBT-I (cognitive behavioural therapy for insomnia)
- Behavioural health patients where poor sleep drives depression, anxiety, PTSD or substance-use relapse risk
- Primary care and integrated care settings needing a two-minute sleep screen
- Any clinician who needs a repeatable outcome measure to show whether sleep treatment is working
Administration and re-testing
- Give the ISI as a self-report. Patients answer for the last two weeks — say that out loud, because people otherwise answer for last night.
- All seven items must be completed for the total to be valid. If an item is skipped, ask for it rather than pro-rating.
- Re-administer every one to two weeks during active sleep treatment, then monthly during maintenance. Insomnia scores move quickly, so short intervals show real change.
- Pair the ISI with a one- to two-week sleep diary when you need objective sleep timing (sleep onset latency, wake after sleep onset, total sleep time). The ISI measures severity; the diary measures behaviour.
Reliability and validity
- Internal consistency is good to excellent, with Cronbach's alpha typically reported between 0.74 and 0.91 across clinical and community samples.
- At a cut-off of 10 the ISI has been reported with roughly 86% sensitivity and 88% specificity for detecting insomnia in community samples; in clinical samples a cut-off of 11 to 15 gives better specificity.
- The ISI correlates moderately with sleep-diary measures and weakly with polysomnography, which is expected: it measures perceived severity, not sleep architecture.
- It is responsive to treatment, with large effect sizes reported after CBT-I, and is used as the primary endpoint in many insomnia trials.
Licensing and use
The ISI is copyrighted by Charles M. Morin. It is widely reproduced in clinical practice and research; commercial redistribution requires permission from the author or publisher.
Frequently asked questions
How do you score the Insomnia Severity Index?
Score each of the seven items from 0 to 4 and add them for a total of 0 to 28. There are no reverse-scored items or subscales. Bands are 0-7 no clinically significant insomnia, 8-14 subthreshold, 15-21 moderate, and 22-28 severe.
What is a normal ISI score?
A total of 0 to 7 is considered no clinically significant insomnia and is the usual remission target after treatment.
What ISI score indicates insomnia?
Use 10 or higher for screening in general populations and 15 or higher to identify moderate-to-severe clinical insomnia in a treatment setting.
Is the ISI free to use?
The ISI is copyrighted by its author. It is very widely used in clinical care and research and is reproduced in many public clinical resources, but commercial redistribution requires permission from the author or publisher.
How often should the ISI be repeated?
Every one to two weeks during active insomnia treatment and monthly during maintenance. Insomnia scores move quickly, so shorter intervals give you usable signal.
What is the difference between the ISI and a sleep diary?
The ISI measures how severe, distressing and impairing the patient perceives their insomnia to be. A sleep diary records actual sleep timing over one to two weeks. Most insomnia assessments use both.
References
- Morin CM, Belleville G, Bélanger L, Ivers H. The Insomnia Severity Index: psychometric indicators to detect insomnia cases and evaluate treatment response. Sleep. 2011;34(5):601-608.
- Bastien CH, Vallières A, Morin CM. Validation of the Insomnia Severity Index as an outcome measure for insomnia research. Sleep Medicine. 2001;2(4):297-307.
- Morin CM. Insomnia: Psychological Assessment and Management. New York: Guilford Press; 1993.
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