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Pack-Years Calculator

Converts a smoking history into pack-years (packs per day × years smoked, 20 cigarettes per pack) and notes the USPSTF lung-cancer screening threshold of 20 pack-years.

When to use

You need a standardised cumulative smoking exposure for risk assessment or screening eligibility.

Do not use when: Exposure is from cigars, pipes, vaping or smokeless tobacco, for which pack-years are not defined.

Formula

pack_years = (cigarettes_per_day / cigarettes_per_pack) × years_smoked

Pack-years summarise dose but not intensity or time since quitting, which also affect risk; periods with different rates should be calculated separately and added. Results are informational only and not a substitute for clinical judgement or medical advice.

Inputs

Parameter	Type	Unit	Required	Description
`cigarettes_per_day`	number		no	Average cigarettes smoked per day. Give this or packs_per_day. Range: ≥ 0, ≤ 200
`packs_per_day`	number		no	Average packs per day (alternative to cigarettes_per_day). Range: ≥ 0, ≤ 10
`years_smoked`	number	years	yes	Total years of smoking at that rate. Range: ≥ 0, ≤ 100
`cigarettes_per_pack`	integer		default 20	Pack size; the pack-year definition uses 20. Range: ≥ 10, ≤ 50

Outputs

Output	Type	Unit	Description
`pack_years`	number	pack-years	packs_per_day × years_smoked.
`packs_per_day`	number		Packs per day used.
`cigarettes_per_day`	number		Cigarettes per day used.
`total_cigarettes`	number		cigarettes_per_day × 365.25 × years_smoked.
`screening_note`	string		Whether the history reaches the 20 pack-year threshold used for lung-cancer screening eligibility (with age 50–80 and quit ≤15 years ago).

Example

20 cigarettes/day for 30 years: {"cigarettes_per_day":20,"years_smoked":30} → {"pack_years":30,"packs_per_day":1,"total_cigarettes":219150}

Half a pack a day for 15 years: {"packs_per_day":0.5,"years_smoked":15} → {"pack_years":7.5,"cigarettes_per_day":10}

GET https://tttkmbb.com/api/v1/calculate/pack-years?cigarettes_per_day=20&years_smoked=30

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/pack-years (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/pack-years · Markdown: https://tttkmbb.com/medical/pack-years.md · JSON definition: https://tttkmbb.com/medical/pack-years.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="pack-years"
OpenAPI operationId: calculate_pack_years
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

NCI Dictionary of Cancer Terms – pack year (government)
USPSTF (2021) Lung Cancer: Screening – recommendation statement (standard)

FAQ

How do I handle changing habits?

Compute each period separately (e.g. 10/day for 5 years = 2.5, then 20/day for 10 years = 10) and add them: 12.5 pack-years.

Is 20 pack-years a hard cut-off?

USPSTF 2021 recommends annual low-dose CT for adults aged 50–80 with at least 20 pack-years who smoke or quit within 15 years; other programmes use different thresholds.

Related calculators

Age Calculator — Age is part of screening eligibility.
VO2 Max Calculator — Cardiorespiratory fitness context.