# Pack Year Calculator

URL: https://speedycalculator.com/calculators/health/pack-years/
Last updated: 2026-10-25

> The pack year calculator measures lifetime tobacco exposure by multiplying packs smoked per day by years of smoking. Pack years are used to decide eligibility for lung cancer screening.

## Inputs

- Cigarettes per day
- Years smoked

## Results

- Pack years

## Formula

```
Pack years = (cigarettes per day ÷ 20) × years smoked
```

## Explanation

One pack year equals smoking 20 cigarettes a day for one year. U.S. guidelines recommend yearly low-dose CT screening for adults aged 50–80 with 20 or more pack years.

### How to use the Pack Year Calculator

- **Cigarettes per day**
- **Years smoked**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Convert cigarettes per day into packs and multiply by the number of years.

### Inputs explained

FieldWhat to enterCigarettes per dayA numberYears smokedA number

### Example values

How the main result changes when **Cigarettes per day** changes and everything else stays at the example values above:

Cigarettes per dayPack years7.59.411.2514.11518.818.7523.422.528.13037.5
*Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.*

## Worked example

Inputs — Cigarettes per day: 15; Years smoked: 25.

Results — **Pack years = 18.8**.

## FAQ

**Does quitting reset pack years?**
No, pack years record past exposure, but risk falls over time after quitting.

**Where can I get help to quit?**
Your doctor or a national quitline can help.

**What formula does the Pack Year Calculator use?**
Pack years = (cigarettes per day ÷ 20) × years smoked.


## Sources

- [U.S. Preventive Services Task Force – Lung cancer screening (2021)](https://www.uspreventiveservicestaskforce.org/uspstf/recommendation/lung-cancer-screening)