A mammogram is an X-ray of the breast used to find cancer early, and the advice on when to start, how often to go and what a result means differs a little between countries. This guide sets out what the Centers for Disease Control and Prevention (CDC), the Food and Drug Administration (FDA) and the National Health Service (NHS) say, with October’s awareness month as a reason to look at it now.
What is a mammogram, and what is it for?
According to the CDC, a mammogram is an X-ray picture of the breast, and it is the best way to find breast cancer for most women of screening age. Regular screening can lower the risk of dying from breast cancer. The NHS describes the same test as a way to look for cancers that are too small to see or feel.
The point of screening is timing. The CDC says more than 99% of women whose breast cancer is found at an early, localized stage are alive five years after diagnosis. That figure describes survival for cancers caught early, not a guarantee for any one person, but it explains why screening programs exist.
Screening is different from diagnosis. Screening tests people with no symptoms. Anyone who notices a lump or another change in the breast should contact a clinician rather than wait for a routine appointment.
When should screening start in the United States?
The CDC says the U.S. Preventive Services Task Force recommends a mammogram every two years for women aged 40 to 74 who are at average risk of breast cancer. Women at higher-than-average risk may be advised to follow a different schedule, and the CDC encourages women to weigh the benefits and risks of screening with their own doctor.
On cost, the CDC says most health insurance plans must cover screening mammograms every one to two years starting at age 40, with no copay, deductible or coinsurance. The agency’s National Breast and Cervical Cancer Early Detection Program offers free or low-cost mammograms to eligible people, which matters for anyone without coverage.
How does the UK approach differ?
The NHS invites people registered with a GP as female for breast screening from age 50 up to their 71st birthday. The first invitation usually arrives between ages 50 and 53, and invitations then come every three years.
| United States (CDC) | United Kingdom (NHS) | |
|---|---|---|
| Ages covered | 40 to 74, average risk | 50 up to the 71st birthday |
| Interval | Every 2 years | Every 3 years |
| How it starts | Discuss with a doctor; insurance covers | Automatic invitation through a GP registration |
| After the upper age | Talk to a doctor | Not invited, but can book every 3 years by calling the local service |
The NHS adds that anyone who has not been invited by 53 and thinks they should have been can contact their local breast screening service. Differences like these reflect how each health system weighs benefits against harms and costs, not a disagreement about whether screening can help.
Which risk factors change the picture?
Age is the biggest one. The CDC notes that most breast cancers are diagnosed after age 50. It lists several risk factors that cannot be changed:
- Inherited gene changes such as BRCA1 and BRCA2
- An early start to menstruation or a late menopause
- Dense breasts
- A personal history of breast cancer or certain non-cancerous breast conditions
- Chest or breast radiation before age 30, for example as treatment for Hodgkin’s lymphoma
- A family history, including a mother, sister or daughter with breast cancer, several relatives, a relative diagnosed young, or ovarian cancer in the family
Others are within a person’s influence: physical inactivity, excess weight after menopause, certain hormone therapies and alcohol use, where risk rises with the amount consumed. A person with a strong family history is a case where the standard schedule may not fit, and a clinician can advise on earlier or additional screening.
What does a dense-breast notice mean?
Breast density describes how the tissue looks on a mammogram, not how the breast feels. The FDA says about half of U.S. women over 40 have dense breast tissue. The agency explains that dense tissue can make cancers harder to see on a mammogram, and that dense breasts are also a recognized risk factor for developing breast cancer.
Reports use four categories:
- Almost entirely fatty
- Scattered areas of fibroglandular density
- Heterogeneously dense, which may hide small masses
- Extremely dense, which lowers the sensitivity of mammography
An FDA rule that took effect in September 2024 requires mammography facilities to give patients a written summary of their density. Women told their breasts are dense are directed to talk with a health care provider about breast density, their risks and their individual situation. For some people with dense tissue, the FDA says, other imaging tests alongside a mammogram may help find cancers. Whether that makes sense is a conversation to have with a clinician, because extra tests can also bring extra false alarms.
What happens at the appointment, and when do results arrive?
According to NHS guidance, each X-ray takes only a few seconds, and the whole appointment should take no more than 30 minutes and is often quicker. Results usually arrive within two weeks of the appointment, though sometimes it takes longer. In the U.S., timing varies by facility, so it is worth asking at the visit how and when results will be shared.
Questions worth asking before the visit
A few practical questions can make the appointment smoother:
- Is this a screening mammogram or a diagnostic one for a specific concern?
- Will prior images be compared, and does the facility need copies from elsewhere?
- How will results and the breast density summary be delivered?
- Does family history or a past biopsy change the recommended schedule?
Bringing a list of relatives who have had breast or ovarian cancer, and the ages at which they were diagnosed, gives the clinician what they need to judge whether the standard schedule fits.
Why might someone be called back after screening?
A callback can be unsettling, so the numbers help. The NHS says that for every 100 people screened, about 4 are asked to return for further tests. Most of those people do not have breast cancer. About 1 of the 4 is diagnosed with the disease, and about 96 in 100 need nothing further.
An illustrative bit of arithmetic scales those figures up. In a group of 1,000 people screened, the NHS proportions would imply roughly 40 callbacks and about 10 diagnoses. These are scaled estimates, not published counts. They show why a recall letter is common and is not itself a diagnosis.
What are the downsides of screening?
The CDC lists several. False positives lead to more testing and anxiety. Overdiagnosis and overtreatment can occur, which the NHS describes as finding cancer that would never have caused harm. Procedures can be uncomfortable, repeated X-rays involve a small radiation dose, and a false negative can delay diagnosis. The NHS says missed cancers happen very rarely, and that the radiation dose very slightly increases lifetime cancer risk.
Other tools have a role in specific cases. The CDC says breast MRI is used alongside mammograms for women at high risk, not average risk, because it often looks abnormal when no cancer is present. Ultrasound and clinical breast exams also exist, and the CDC recommends breast self-awareness, meaning knowing how your breasts normally look and feel so that changes can be reported.
Making sense of the guidance
Screening guidance gives a framework, not a personal verdict. The U.S. starts at 40 with a two-year interval, the UK at 50 with a three-year interval, and both rely on the same test. What matters most is knowing which category applies to you, such as average risk, a strong family history or dense breasts, and checking that with a clinician. For related reading on prevention-minded habits, see how prediabetes numbers are read, when flu shots make sense this season and how telehealth is changing access to care.
This article is general information, not medical advice. Talk to a qualified health professional about your own screening needs.
Sources: Centers for Disease Control and Prevention; U.S. Food and Drug Administration; National Health Service; GOV.UK
