A CT calcium score tells you how much calcified plaque has built up in the arteries that supply blood to your heart. It’s a direct measurement of atherosclerosis, the disease process behind most heart attacks, and it gives you a single number that reflects your personal risk. A score of zero means no detectable calcium and a low chance of heart attack in the coming years, while scores above 300 signal extensive plaque buildup and significantly higher risk.
How the Score Is Calculated
The scan itself takes about 10 minutes and doesn’t require any contrast dye or injections. A CT scanner captures images of your heart, and software identifies bright spots of calcium in the walls of your coronary arteries. Each deposit is measured by size and density, and the results are added up into a single number called the Agatston score. That number is your calcium score.
Your report will also typically include a percentile ranking that compares your score to other people of the same age, sex, and race. A 55-year-old man with a score of 50 is in a very different position than a 55-year-old woman with the same number, because men tend to develop coronary calcium earlier. The percentile tells you whether your plaque burden is above or below what’s expected for someone like you. These percentiles were originally developed from the Multi-Ethnic Study of Atherosclerosis (MESA), a large population database that remains the most widely used reference.
What Each Score Range Means
Calcium scores fall into four broad risk categories:
- 0: No detectable calcium. Very low risk of heart attack. This is sometimes called the “power of zero” because it’s strongly reassuring.
- 1 to 99: Mild plaque buildup. Mildly increased risk. Plaque is present, but the burden is still relatively small.
- 100 to 299: Moderate plaque deposits. Associated with a relatively high risk of heart attack or other heart disease over the next three to five years.
- 300 or higher: Extensive plaque. Moderate to severely increased risk, and a sign that coronary artery disease is well established.
These categories are useful starting points, but context matters. A score of 85 in a 40-year-old is far more concerning than the same score in a 75-year-old, because the younger person has accumulated more plaque than expected for their age. That’s why the percentile ranking often carries as much weight as the raw number.
What a Zero Score Does and Doesn’t Guarantee
A score of zero is one of the most powerful pieces of reassurance in preventive cardiology. It means the scan detected no calcified plaque in your coronary arteries, and your near-term risk of a heart attack is very low. For many people, a zero score is reason to hold off on starting a cholesterol-lowering medication and instead focus on lifestyle measures.
That said, a zero score doesn’t rule out heart disease entirely. Not all plaque is calcified. Younger, “softer” plaques made up of fat and cholesterol can narrow arteries or rupture without containing any calcium at all. Research comparing calcium scoring to full CT angiography (a more detailed scan that visualizes the artery walls with contrast dye) found that among patients who had confirmed blockages, a large number had calcium scores that would not have flagged them. A zero score has a low prevalence of obstructive disease, but it cannot exclude a blockage caused by non-calcified plaque. This limitation is most relevant if you already have symptoms like chest pain or shortness of breath. In that case, your doctor will typically order a more detailed test rather than relying on the calcium score alone.
Who Benefits Most From the Test
The calcium score is most useful as a tiebreaker. If your estimated 10-year risk of heart disease falls in the intermediate range (roughly 5% to 20%), the score can push the decision about preventive treatment in one direction or the other. A score of 100 or higher in this group supports starting a statin, while a score of zero is reason to defer or delay medication.
If your risk is already clearly high (you have diabetes, very elevated cholesterol, or a strong family history and other risk factors), you’ll likely benefit from treatment regardless of what the scan shows. And if your risk is very low, the scan is unlikely to change your management. The sweet spot is that middle ground where traditional risk calculators leave room for uncertainty. In that scenario, the calcium score outperforms other screening markers, including C-reactive protein blood tests, carotid artery ultrasound, and ankle blood pressure ratios.
People with a family history of early heart disease sometimes pursue the test even when their calculated risk is low, since standard risk tools don’t fully account for genetics. A surprise finding of calcium in a 40-year-old with a “clean” risk profile can change the conversation entirely.
What the Scan Cannot Tell You
The calcium score measures how much plaque exists, not how much it’s blocking blood flow. Two people with a score of 200 could have very different anatomy: one might have calcium spread thinly across several arteries with no significant narrowing, while the other might have a tight blockage in a single vessel. If your doctor needs to know whether a specific artery is obstructed, a CT angiography (CTA) is the next step. Studies show CTA has significantly higher accuracy for detecting obstructive coronary artery disease (about 81%) compared to the calcium score alone (about 69%).
The scan also only detects calcified plaque. Soft, non-calcified plaques, which are actually more likely to rupture and cause acute heart attacks, don’t show up on a standard calcium scan. This is a key nuance: the calcium score is a marker of your total plaque burden over time, not a direct snapshot of your most dangerous lesions. A high score tells you that atherosclerosis is active and widespread, which in turn raises the probability that vulnerable plaques are also present. But the scan itself cannot identify them.
Radiation, Cost, and Practical Details
A cardiac calcium scan delivers a radiation dose with a median of about 2.3 millisieverts, though it can range from under 1 to over 10 depending on the machine and protocol used. For comparison, a standard chest X-ray delivers roughly 0.02 millisieverts, so a calcium scan exposes you to meaningfully more radiation, though still a fraction of what you’d receive from a full diagnostic CT of the chest. For a one-time or occasional screening test, the dose is generally considered acceptable, but it’s one reason the scan isn’t recommended as a routine annual test for everyone.
Insurance coverage varies. Many plans don’t cover the scan when it’s ordered as a screening test in people without symptoms. Out-of-pocket costs typically range from $100 to $400. Some imaging centers and hospitals offer it as a self-pay option at the lower end of that range, and it doesn’t require a referral in all states.
What Happens After You Get Your Results
A score of zero with no symptoms generally means you can revisit the conversation in five to ten years. Plaque develops slowly, and a zero score has a long “warranty period” during which your risk stays low.
If your score is above zero, the number becomes part of your overall risk picture. Scores in the 1 to 99 range often prompt closer attention to diet, exercise, blood pressure, and cholesterol, with medication considered depending on other factors. Scores of 100 or above typically shift the balance toward starting a statin, since they indicate enough plaque accumulation that the benefit of treatment outweighs the cost and side effects. Scores above 300 almost always lead to aggressive risk-factor management and sometimes additional testing to check for significant blockages.
One thing the score does especially well is motivate behavior change. Seeing a concrete number attached to plaque in your arteries tends to make the abstract concept of heart disease feel personal. Studies have shown that patients who see their calcium scores are more likely to follow through on lifestyle changes and stick with prescribed medications than those who only hear about their statistical risk.