The short answer: A screening mammogram is a routine check for women with no breast symptoms. It takes two standard X-ray views of each breast, and a radiologist reads it later. A diagnostic mammogram is a problem-solving exam. It is ordered when you have a lump, nipple discharge, or an unclear finding on a screening mammogram. The technologist takes extra views, the radiologist reads the images while you wait, and an ultrasound is often added. Screening is usually free under your insurance. Diagnostic mammograms usually carry a copay, coinsurance, or deductible.
Who gets a screening mammogram?
Screening is for women who feel fine and have no breast complaints. The Medicare coverage rule for breast imaging defines it as an exam "furnished to a woman without signs or symptoms of breast disease, for the purpose of early detection of breast cancer." The same rule states that the exam is "inherently bilateral." Both breasts are imaged every time.
The 2024 USPSTF recommendation advises screening every two years for women ages 40 to 74 at average risk. This is a Grade B recommendation. The National Cancer Institute notes that some high-risk groups start earlier. Women who had chest radiation for a childhood cancer may begin at age 25. If you are unsure when to start, read our guide on when to get your first mammogram.
You do not need a doctor's order for a screening mammogram. The Medicare rule states that "a physician's referral is not required for a screening mammography." Many imaging centers let you book one directly.
When do you need a diagnostic mammogram instead?
A diagnostic mammogram answers a specific question about your breast. Medicare lists the main reasons it is indicated:
- Signs or symptoms that could point to cancer, such as a mass, some types of spontaneous nipple discharge, skin changes, pain in one breast, or swollen lymph nodes under one arm.
- An abnormality found on a screening mammogram.
- A personal history of breast cancer that needs follow-up imaging.
MedlinePlus adds two more situations. Diagnostic imaging is used when you have breast implants, or when something else makes your breast tissue hard to see. Age matters too. The ACR Appropriateness Criteria for palpable breast masses say ultrasound is usually the first test for women under 30. For women 40 and older, diagnostic mammography or tomosynthesis is the first test.
A diagnostic mammogram needs a referral from your doctor or nurse practitioner. There is one exception. If the radiologist sees a problem on your screening images the same day, the Medicare rule lets them add diagnostic views "without an additional order from the treating physician." A new lump or skin change is always worth a call to your doctor. If you want help sorting out breast symptoms before that visit, symptom.md covers the common ones.
What does the technologist do differently?
A screening exam is fixed and quick. The American Cancer Society describes it as pictures of each breast "typically from 2 different angles." Medicare names those two views: craniocaudal (top to bottom) and mediolateral oblique (angled from the side). Four images in total. The technologist follows the same protocol for everyone.
A diagnostic exam is tailored to your problem. The technologist starts with the standard views if you have not had them recently. Then the radiologist directs extra pictures. The ACR palpable mass guideline lists the common ones:
- Spot compression views. A small paddle presses on one area to spread out tissue. This shows whether a shadow is a real mass or overlapping normal tissue.
- Magnification views. These enlarge a small region to show the shape and pattern of calcifications.
- Tangential views. These confirm whether a finding sits in the skin or deeper in the breast.
- Extra angles. Exaggerated craniocaudal, cleavage, and 90-degree lateral views help locate a finding in three dimensions.
Because more images are taken, the exam takes longer and the radiation dose is higher. The National Cancer Institute states that "diagnostic mammography requires images from more angles than screening mammography, so the dose of radiation is higher." The dose is still low. Many centers now use 3D mammography for both exam types, which can reduce the need for some extra views.
How does the radiologist read each exam?
Screening mammograms are read in batches, often hours or days after your visit. You go home without a result. Under the FDA Mammography Quality Standards Act rules in force since September 10, 2024, the facility must send you a plain-language letter. If the result is "Suspicious" or "Highly Suggestive of Malignancy," you and your doctor must be notified within 7 calendar days. That letter must also tell you whether your breasts are dense. Our dense breast guide explains what to do with that information.
Diagnostic mammograms are read while you wait. The radiologist looks at each image as it is taken and decides whether more views are needed. The American Cancer Society states that "you will most likely be given the results of your tests during the visit." An ultrasound is often added in the same appointment. Medicare covers a breast ultrasound when a provider orders it to check a specific area.
The two exams also end with different labels. A screening exam that needs more work-up is coded BI-RADS 0, "Incomplete: Need additional imaging evaluation." A diagnostic exam must end in a final assessment: benign, probably benign, suspicious, or highly suggestive of malignancy. Our BI-RADS guide walks through each category.
How often does screening lead to a diagnostic exam?
Callbacks are common and usually benign. In the Breast Cancer Surveillance Consortium benchmarks for 3D screening from 2011 to 2018, 8.3% of screening exams were flagged for more imaging. Cancer was found in 5.8 of every 1,000 screens. The American Cancer Society reports that "fewer than 1 in 10 women called back for more tests are found to have cancer." Callbacks are more common after a first mammogram, because there are no older images for comparison. Read our mammogram callback guide for what to expect at that visit.
Diagnostic exams find cancer far more often, because the patients already have a finding. In the BCSC diagnostic benchmarks covering 401,548 exams from 2007 to 2013, the cancer detection rate was 34.7 per 1,000. For diagnostic exams done to evaluate a lump, it was 64.5 per 1,000. Even so, most diagnostic exams end without a cancer diagnosis.
What do the two exams cost?
This is where the label on your order matters most. The National Cancer Institute explains that insurance plans governed by the Affordable Care Act "must cover screening mammograms as a preventive benefit every 1–2 years for women ages 40 and over without requiring copayments, coinsurance, or deductibles." Medicare Part B covers one screening mammogram every 12 months for women 40 and older. You pay nothing if the provider accepts assignment. Medicare also covers one baseline mammogram between ages 35 and 39.
Diagnostic mammograms are treated as medical care, not prevention. Under Medicare, "after you meet the Part B deductible, you pay 20% of the Medicare-approved amount." Private plans vary, so ask your plan before the visit. Medicare does allow diagnostic exams more than once a year when they are medically necessary.
The billing codes explain the split. Per the AAPC CPT code listing, CPT 77067 is bilateral screening mammography, including computer-aided detection when performed. CPT 77066 is bilateral diagnostic mammography. CPT 77065 is diagnostic mammography of one breast. When a screening exam converts to a diagnostic exam on the same day, Medicare allows the facility to bill both codes.
The bottom line
Screening mammograms are for women with no symptoms. They use two standard views per breast, are read later, and cost nothing under most plans. Diagnostic mammograms answer a specific question. They add spot compression, magnification, or extra angles, are read on the spot, and often include an ultrasound. They also carry cost sharing. Most callbacks and most diagnostic exams end without a cancer diagnosis. If you have a lump or a new breast change, ask for a diagnostic exam, not a screening one.
Last updated: August 2026. This article is for informational purposes only and does not constitute medical advice. Talk with your doctor or a breast imaging radiologist about which mammogram is right for you and about any new breast symptom.