What your pack year result means

What does the number measure?

One pack year is 20 cigarettes a day for one year. A result of 10 pack years means the history adds up to the same number of cigarettes as 20 a day for 10 years; the calculator says this in words under the result. Other tobacco is converted to cigarettes first, as set out in how the calculation works.

The result screen shows the total rounded to the nearest whole number and a breakdown by type of tobacco.

What does it not tell you?

The calculator puts it plainly: “Pack years are a record of past smoking, not a diagnosis. They do not tell you whether you have a lung condition.” It gives general information, not personal clinical advice, and it cannot tell you what your own number means for your health.

The measure also has limits. FAQ 2 calls it “only a crude imprecise description of smoking related exposure”: 5 cigarettes a day for 20 years and 20 a day for 5 years are both 5 pack years, but FAQ 2 says the risk of smoking-related ill health is very much greater in the first case. In 2023 Dr Masters wrote: “The number of cigarette pack years is still widely used by clinicians but has drawbacks. Years smoked and active smoking are the most useful terms to ascertain risk.”

The calculator does not count passive smoking or vaping, and its conversion figures are approximations (see the References page).

How have clinicians used pack years?

The FAQs explain that numbers in a patient’s record can be searched to identify at-risk groups, in the same way as blood pressure readings or body mass index. They recommend recording pack years alongside starting and stopping dates and years smoked.

What is the 15 pack year approach in FAQ 4?

FAQ 4 describes one practice that used smoking load, rather than symptoms, to decide whom to invite for spirometry, a test that measures how much air you can breathe out in one breath. The aim was to help detect chronic obstructive pulmonary disease (COPD). In FAQ 4’s words:

• “Current and ex-smokers over 40 with 15 pack years or more were invited for spirometry screening entitled ‘a free lung check’.”
• “After 10 months, 56% of this group had their smoking load recorded, and 45% of those had had spirometry.”
• “Patients found this way made up 35% of the practice’s COPD register, a 54% increase.”

The work was published as Masters N, Tutt C, Eades J, “Early diagnosis of COPD”, Br J Gen Pract 2006;56:969. NICE guidance on COPD (NG115) sets no pack-year threshold: it says to suspect COPD in people over 35 with a risk factor such as smoking, and asks for pack years to be recorded for everyone with COPD.

This was one practice’s way of choosing whom to invite. A result above or below 15 does not tell you whether you have a lung condition. Pack years and COPD sets out the 2006 work and the NICE guidance in more detail.

How are pack years used in lung cancer screening?

In England, NHS lung health checks invite people aged 55 to 74 who have ever smoked, and use a risk assessment, rather than a pack-year cut-off, to decide who is offered a scan. In 2023 Dr Masters wrote that the screening programme would use the codes ex-smoking, smoking and intensity of smoking to decide who should be offered screening, and that these codes are descriptive and difficult to search.

In the United States, the US Preventive Services Task Force recommended in 2021 lung cancer screening for adults aged 50 to 80 who have a smoking history of at least 20 pack years and who smoke now or stopped within the past 15 years.

For what 20 pack years represents, see is 20 pack years a lot? Screening programmes ask their own questions and decide who is invited. If you are worried about your health, speak to your GP practice or use NHS 111.