A normal coronary calcium score is zero. That means no detectable calcium buildup was found in the arteries that supply blood to your heart. The score comes from a quick CT scan of your chest and is measured in Agatston units (AU), a scale that starts at zero and has no upper limit. Any score above zero indicates at least some calcified plaque in your coronary arteries, though the level of concern depends on how high the number goes and factors like your age and sex.
What the Score Ranges Mean
The coronary artery calcium (CAC) score is divided into broad tiers that reflect how much calcified plaque has accumulated in and around your artery walls. According to Mayo Clinic classifications:
- 0: No calcium detected. This is the ideal result and is associated with a very low risk of heart attack over the next decade.
- 1 to 99: Mild plaque deposits. Some calcium is present, but the amount is small.
- 100 to 300: Moderate plaque deposits. At this level, the risk of a future cardiac event rises meaningfully.
- Above 300: Extensive calcification, signaling more advanced coronary artery disease and a higher heart attack risk.
Data from a large American Heart Association study tracked 10-year rates of cardiovascular events across these tiers. People with a score of zero had roughly a 2.7% chance of a major event over a decade. That jumped to about 7% for scores of 1 to 99, and to 16.5% for scores of 100 and above. The pattern held across different racial and ethnic groups and for both men and women.
Why a Zero Score Isn’t a Perfect Guarantee
A score of zero is strongly reassuring, but it doesn’t mean your arteries are completely free of plaque. The scan only detects calcified (hardened) plaque. Softer, non-calcified plaque doesn’t show up on the scoring scan at all. Research published in the Journal of Cardiovascular Computed Tomography found that a meaningful percentage of people with a zero calcium score still had non-calcified plaque, including about 8.4% with features considered higher risk. That said, the overall predictive power of a zero score remains strong. People who score zero consistently have low event rates regardless of the presence of soft plaque, which is why cardiologists still consider it one of the most valuable screening results available.
How Age, Sex, and Ethnicity Affect “Normal”
Calcium naturally accumulates in arteries over time, so a score that would be unusual for a 45-year-old might be perfectly typical for someone in their 70s. Men also tend to develop coronary calcium earlier and in greater amounts than women. The Multi-Ethnic Study of Atherosclerosis (MESA), a major federally funded research project, built a reference tool that compares your individual score against people of the same age, sex, and racial or ethnic background. If your score falls at or above the 75th percentile for your demographic group, it’s considered elevated even if the raw number seems modest.
For example, a calcium score of 50 in a 48-year-old woman could place her well above the 75th percentile, flagging meaningful risk. The same score in a 72-year-old man might land at a much lower percentile and carry a different clinical significance. This is why the raw number alone doesn’t tell the full story.
How Scores Guide Treatment Decisions
The calcium score is most useful for people whose heart disease risk falls into a gray zone. The 2019 ACC/AHA prevention guidelines specifically recommend the scan for adults at intermediate risk (roughly a 7.5% to 20% estimated 10-year risk of a cardiovascular event) and sometimes for those at borderline risk (5% to 7.5%). For these groups, the scan can push the risk estimate meaningfully up or down and help clarify whether starting a cholesterol-lowering medication like a statin makes sense.
The thresholds are straightforward. A score of 100 or higher, or a score at or above the 75th percentile for your age, sex, and ethnicity, generally supports starting statin therapy. A score of zero shifts the calculus in the opposite direction, suggesting that statins may offer limited benefit for the time being. Scores between 1 and 99 fall into more nuanced territory. In that range, the 10-year event rate varies by age: about 3.8% for adults 45 to 54, 6.5% for those 55 to 64, and 8.3% for those 65 to 74.
What the Scan Involves
A coronary calcium scan is a specialized CT scan that takes about 10 to 15 minutes. You lie on a table while the scanner captures images of your heart, timed to your heartbeat. No contrast dye is injected, and no needles are involved. The radiation exposure is low, around 1 to 2 millisieverts, roughly equivalent to one to two years of natural background radiation. For comparison, a standard chest CT delivers about 10 millisieverts, so the calcium scan uses a fraction of that dose.
Most insurance plans do not cover the scan for screening purposes, though some do when ordered for specific clinical reasons. Out-of-pocket costs typically range from $75 to $300 depending on your location and facility.
When to Repeat the Scan
If your score comes back at zero, major cardiology guidelines recommend waiting 5 to 10 years before repeating the test. The European Society of Cardiology advises no repeat scan sooner than five years from the initial one. This long interval reflects just how stable a zero score tends to be: most people who score zero don’t develop significant calcification within a few years, particularly if their other risk factors remain controlled. If your score is above zero, the decision about repeat scanning is more individualized and depends on how aggressively risk factors like cholesterol and blood pressure are being managed.