Check your BMI — and what it means for cancer risk
Most BMI calculators give you a number and stop. This one adds the context we exist to share: how a healthy weight relates to your risk of cancer. It is information to act on calmly — not medical advice, and never a diagnosis.
Why is a cancer charity asking about your weight?
Because the evidence is strong and strangely little known. According to Cancer Research UK, after smoking, carrying excess weight is the second biggest preventable cause of cancer in the UK, and it is linked to 13 different types of the disease. Sharing that calmly, without fear, is part of what we do.
The short version
- Excess weight is the UK's second biggest preventable cause of cancer, after smoking.
- It is linked to 13 cancer types, including bowel, breast and womb.
- More than 1 in 20 UK cancer cases are linked to it, yet around 3 in 4 adults do not know the link exists.
- A higher weight raises risk across a population; it is not a diagnosis, and a healthy weight is not a guarantee.
- Weight is one of several things you can influence, alongside not smoking, alcohol, diet and activity.
Most people can name smoking as a cause of cancer. Far fewer know what comes second. Cancer Research UK surveys have found around three in four UK adults are unaware that excess weight raises cancer risk at all, which is exactly why a tool like this needs to exist.
More than one in twenty cancer cases in the UK are linked to being overweight or obese. That is not a reason to panic. It is a reason to pay attention, because unlike many causes of cancer, weight is something many of us can influence, and the benefit of small, steady change begins long before any big shift on the scales.
The 13 cancers linked to excess weight
Source: Cancer Research UK. The tool above shows which of these are most relevant to you.
How does excess weight affect cancer risk?
It is biology, not blame. According to Cancer Research UK, body fat is not inert: it raises levels of growth hormones and insulin that push cells to divide more often, keeps the body in a state of low-level inflammation, and, after the menopause, produces extra oestrogen. Over years, each of these makes faulty cell growth a little more likely.
Growth signals
Excess fat raises growth hormones and insulin, which tell cells to divide more often than they need to.
Inflammation
It keeps the body in a state of quiet, low-level inflammation, a background state linked with several cancers.
Extra oestrogen
After the menopause, fat tissue makes extra oestrogen, which raises the risk of breast and womb cancers.
How should you read your result?
Read it as a signpost, not a verdict. BMI is a screening number: it flags whether your weight might be affecting your health, but it cannot see muscle, where fat is carried, or how you feel. If your result sits in the healthy range, there is nothing to act on from the number alone. If it sits above, treat it as a prompt for a calm conversation, not an alarm.
The tool adds the context a bare number leaves out: your healthy weight range in pounds or kilograms, an optional waist reading, and the weight-related cancers most relevant to you. A pharmacist can talk any of it through without an appointment, and a GP can look at the fuller picture. When you are ready to go further, our prevention guides cover the everyday changes that lower risk most.
Please hold all of this lightly. Risk across a population is not a forecast for you. A higher weight does not mean you will get cancer, and a healthy weight is no guarantee against it. If your reading concerns you, a pharmacist can help without an appointment and a GP can look at the fuller picture. This page informs; it does not diagnose.
Common questions
Is this medical advice?
No. It is information to help you understand a number, not a diagnosis or a treatment plan. BMI is a screening signal — a starting point for a conversation with a pharmacist or GP, not a conclusion on its own.
Why is a cancer charity asking about my weight?
Because after smoking, carrying excess weight is the second biggest preventable cause of cancer in the UK, and it is linked to 13 different cancer types. Yet surveys suggest most people are unaware of the link. Raising that awareness — calmly, without alarm — is part of our mission.
Does a high BMI mean I will get cancer?
No. These are patterns across whole populations, not a prediction about any one person. A higher weight raises risk on average; it does not make cancer certain, and a healthy weight is not a guarantee against it. Weight is one of several things you can influence.
What is a healthy BMI range?
For most adults, a BMI between 18.5 and 24.9 is considered the healthy range, with 25 to 29.9 counted as overweight and 30 or above as obese (NHS). NICE recommends lower cut-offs for people of South Asian, Black African, African-Caribbean and Middle Eastern family origin, where a healthy BMI ends around 23. The tool applies the right range for you.
Does losing weight actually reduce cancer risk?
Reaching and keeping a healthy weight is one of the most effective things people can do to lower their risk of cancer, according to Cancer Research UK and the World Cancer Research Fund. You do not need dramatic weight loss to benefit, and the gains from being more active and eating well begin before the scales move much. It lowers risk; it cannot remove it entirely.
Is my data private?
Completely. The tool runs entirely in your browser. There is no account, nothing is saved, and nothing you type is ever sent to us or anyone else. Close the tab and it is gone.
Why does it ask about sex and ethnic background?
Both change how the numbers are read, following published guidance. Waist thresholds differ by sex, and some weight-related cancers affect only women. NICE also recommends lower BMI thresholds for people of South Asian, Black African, African-Caribbean and Middle Eastern family origin, who tend to develop weight-related health problems at a lower BMI. Both questions are optional.
Where these figures come from
Every number in this tool is drawn from published UK guidance and the leading cancer-prevention research bodies. It is not affiliated with, or endorsed by, the NHS.