How this instrument works
The Heaviness of Smoking Index scores nicotine dependence from two questions: how many cigarettes someone smokes per day, and how long after waking the first cigarette is lit. Each question is scored 0 to 3, and the two scores are added directly, giving a total that runs 0, least dependent, to 6, most.
It was built as a shortcut from the longer Fagerström Test for Nicotine Dependence, a six-item questionnaire this site also hosts as a separate calculator. Kozlowski and colleagues tested whether a stripped-down version could predict smoking-cessation difficulty nearly as well as the full scale, and found that cigarettes-per-day and time-to-first-cigarette carried most of that predictive power on their own — the other four items added comparatively little once those two were already known.
Time-to-first-cigarette does the heavier lifting of the pair. Overnight sleep is the longest stretch a regular smoker's body typically goes without nicotine, so how urgently someone reaches for a cigarette after that gap — within 5 minutes versus after an hour — reflects the depth of physical dependence more directly than the day's raw count does. That is why it carries the same 0-to-3 weight as cigarettes-per-day despite being a single moment rather than a running tally.
- Select Cigarettes smoked per day — the four bands run from 10 or fewer up to 31 or more.
- Select Time to first cigarette after waking — from within 5 minutes up to after 60 minutes.
- Read the Heaviness of Smoking Index: the two selections add directly, with no further arithmetic.
- A total of 0-1 suggests low dependence, 2-4 moderate, and 5-6 high; see the FAQ for how this maps to the longer FTND.
Worked example — 21-30 cigarettes a day, first one within 5 minutes
Someone smoking 21 to 30 cigarettes a day scores 2 on that item. Lighting the first cigarette within 5 minutes of waking scores 3, the maximum on that item. Add them: 2 + 3 = 5, out of a possible 6, near the top of the scale, and a pattern the original validation study linked to heavier physical dependence.
Compare two other cases computed the same way. Smoking 10 or fewer a day and waiting more than 60 minutes for the first one scores 0 + 0 = 0, the floor of the scale. Smoking 31 or more a day and lighting up within 5 minutes scores 3 + 3 = 6, the ceiling, the two extremes the 7-point (0-6) scale was built to span.
Questions
How does the HSI compare to the full Fagerström Test for Nicotine Dependence?
Kozlowski and colleagues found that this 2-item version predicts smoking-cessation difficulty about as well as the full 6-item FTND, using only the two questions that carried most of the longer test's predictive power. It trades a small amount of precision for speed, useful when a fast screen matters more than the extra detail the other four FTND questions add.
Why these two questions specifically, out of the six on the FTND?
Cigarettes per day and time to first cigarette after waking turned out, in the original analysis, to explain most of the variation the full scale explained on its own. The other four FTND items, such as difficulty refraining in no-smoking areas or which cigarette would be hardest to give up, added comparatively little once those two were already known, so the shorter index kept only the pair doing the heaviest work.
Why does time to first cigarette matter so much?
Overnight sleep is typically the longest stretch a regular smoker goes without nicotine. How quickly someone reaches for a cigarette after that gap, a proxy for how urgently withdrawal sets in, tracks physical dependence more directly than the day's raw cigarette count, which is also shaped by things like cost, workplace rules, and social setting.
What does a score of 5 or 6 mean?
It places someone in the high-dependence band of the 0-6 range, associated in the original study with greater difficulty quitting and a higher relapse rate among those who attempt it. It is a research-derived proxy, not a diagnosis; clinicians use it alongside a conversation about quitting history, triggers, and support, not as a standalone verdict.
Can the HSI be used for products other than cigarettes?
Not directly. It was validated specifically on cigarette smoking, and the two questions, cigarettes per day and time to first cigarette, do not map cleanly onto vaping, smokeless tobacco, or other nicotine products, which have different use patterns. Dependence scales for those products exist separately and are not interchangeable with this one.
Is a low HSI score a reason to not worry about quitting difficulty?
No. It is a statistical association from population data, not a guarantee for any one person. Someone scoring 0 or 1 can still find quitting hard, and factors the HSI does not measure, such as stress, social smoking, or other substance use, matter too. Treat it as one data point a clinician might use, not the complete picture.
References
- Kozlowski et al. 1994, Drug Alcohol Depend — original validation study (PubMed)
- CDC — Smoking Cessation: Fast Facts
Read this first: This instrument computes a screening figure from population formulas — it is not a diagnosis, and it cannot see the whole picture a clinician can. Use it to inform a conversation, not to replace one.