ISI Score Interpretation: How to Score the Insomnia Severity Index
The Insomnia Severity Index takes about two minutes to complete and under a minute to score: seven items, each 0 to 4, added for a total out of 28. What takes judgement is deciding which cut-off you are using and what a change in score actually means.
This page walks through the arithmetic with a worked example, then sets out the four severity bands, the two competing cut-offs, and the change thresholds used in insomnia treatment.
Step-by-step scoring
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.
A worked example
| Item | Response and score |
|---|---|
| 1a. Difficulty falling asleep | Severe = 3 |
| 1b. Difficulty staying asleep | Moderate = 2 |
| 1c. Waking too early | Mild = 1 |
| 2. Satisfaction with sleep | Dissatisfied = 3 |
| 3. Interference with daily functioning | Much = 3 |
| 4. Noticeable to others | Somewhat = 2 |
| 5. Worried or distressed about sleep | Much = 3 |
Total = 3 + 2 + 1 + 3 + 3 + 2 + 3 = 17, which falls in the 15-21 band: moderate clinical insomnia. CBT-I is indicated, and the treatment target is a total below 8 with at least a 6-point reduction.
Score ranges and what to do next
| Score | Severity | Next step |
|---|---|---|
| 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. |
Scoring mistakes to avoid
- Answering for last night instead of the past two weeks — say the timeframe out loud before the patient starts.
- Pro-rating a missing item. Ask for it; a six-item total is not comparable to anything.
- Switching cut-offs between visits. Pick 10 (screening) or 15 (clinical) per service and keep it.
- Reading a 1-2 point drop as improvement. Meaningful change on the ISI is around 6 points.
- Treating a high score as primary insomnia without screening for sleep apnoea, restless legs, or a circadian shift.
What individual 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.
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Scoring reference for clinicians and patients. Not medical advice, and no score is a diagnosis. See our medical disclaimer.