How to Calculate Insomnia Severity Index
What is Insomnia Severity Index?
The Insomnia Severity Index (ISI) Calculator scores 7 items rated 0-4 to measure the nature, severity, and impact of insomnia, serving as both a screening tool and treatment outcome measure.
Formula
ISI Total = Sum of 7 items (each 0-4); Range: 0-28
- TS
- Total ISI Score (points (0-28)) — Sum of all 7 items indicating insomnia severity
- Qi
- Item Score (points (0-4)) — Rating from 0 (none) to 4 (very severe) for each dimension
- SL
- Severity Level (category) — None (0-7), Subthreshold (8-14), Moderate (15-21), Severe (22-28)
Step-by-Step Guide
- 1Rate 7 items on a 0-4 scale covering: difficulty falling asleep, staying asleep, early awakening, sleep satisfaction, daytime impairment, noticeability of impairment, and distress about sleep
- 2Sum all 7 items for a total score of 0-28
- 3Severity categories: 0-7 no clinically significant insomnia, 8-14 subthreshold insomnia, 15-21 moderate insomnia, 22-28 severe insomnia
- 4A change of 6+ points indicates clinically meaningful improvement
Worked Examples
Input
Moderate difficulty falling asleep (2), moderate difficulty staying asleep (2), mild early waking (1), quite dissatisfied (3), moderately noticeable (2), moderate impairment (2), moderately distressed (2)
Result
ISI score: 14/28 — subthreshold insomnia (8-14); consider sleep hygiene intervention and monitoring
Input
All items rated 3 (quite a bit / very)
Result
ISI score: 21/28 — moderate clinical insomnia (15-21); recommend CBT-I or pharmacotherapy evaluation
Common Mistakes to Avoid
- ✕Using subjective sleep quality alone without considering the daytime impairment and distress items which are equally important
- ✕Not recognizing that an ISI change of 6 points (not just 1-2 points) constitutes reliable clinical improvement
- ✕Assuming insomnia severity correlates directly with hours of sleep — many insomnia patients sleep 6+ hours but with poor quality
Frequently Asked Questions
What ISI score means I have insomnia?
A score of 15 or above indicates moderate clinical insomnia warranting treatment. Scores of 8-14 suggest subthreshold insomnia where sleep hygiene and behavioral interventions may help prevent progression.
What is the best treatment for insomnia?
Cognitive Behavioral Therapy for Insomnia (CBT-I) is the first-line treatment recommended by all major medical guidelines. It is as effective as medication short-term and superior long-term, with typical ISI reductions of 8-12 points.
Ready to calculate? Try the free Insomnia Severity Index Calculator
Try it yourself →