Atrial fibrillation (AFib) affects roughly 1 in 22 American adults, making it the most common heart rhythm disorder in the world. That translates to at least 10.55 million people in the United States alone, and an estimated 52.55 million people globally as of 2021.
Those numbers are growing fast. The global count has risen 137% since 1990, driven largely by aging populations and rising rates of obesity and high blood pressure. In the U.S., the number of people with AFib is projected to reach 12.1 million by 2030 and could triple from 2010 levels by 2050.
Prevalence by Age
Age is the single biggest factor in how likely you are to develop AFib. Among adults under 50, only about 0.26% have the condition. That number climbs steeply with each decade of life, reaching roughly 25% of adults aged 90 and older. The overall prevalence across all U.S. adults sits at about 3.9% to 4.5%, depending on the study and year.
This steep age curve is one reason AFib numbers are projected to keep rising. As the baby boomer generation ages and life expectancy continues to increase, a larger share of the population falls into the high-risk age brackets. AFib isn’t just a disease of the very old, but it becomes dramatically more common after 65.
Men vs. Women
AFib is more frequently diagnosed in men. In one large study tracking participants over five years, 4% of men developed AFib compared to 3.2% of women. That pattern holds across most research, and men are generally considered to be at higher risk.
The picture is more complicated than it appears, though. A National Heart, Lung, and Blood Institute analysis found that the male-female gap partly depends on how researchers account for body size. When BMI was used to adjust for body composition, men appeared to have the greater risk. But when height was used instead, women actually appeared to be at higher risk. This suggests that the commonly reported gender gap may be partly an artifact of how studies are designed rather than a straightforward biological difference.
Differences Across Race and Ethnicity
In the U.S., AFib diagnosis rates are highest among White individuals and lowest among Black individuals, with Hispanic and Asian populations generally falling in between. Studies also show that American Indian and Alaska Native individuals may have a higher risk than any other group, though research in these populations remains limited.
There’s a critical catch to these numbers. Much of the reported gap may reflect differences in who gets tested rather than who actually has AFib. Researchers in one major study compared standard clinical detection with two weeks of continuous heart monitoring across racial groups. Clinically detected AFib was substantially lower in Black individuals compared to White individuals, consistent with the usual pattern. But when the same people wore ambulatory monitors, the prevalence was strikingly similar across all groups: 7.1% in White, 6.4% in Black, 6.9% in Hispanic, and 5.2% in Chinese participants. Those differences were not statistically significant.
Other research using 48-hour monitoring still found White individuals had roughly twice the prevalence of Black individuals (5% vs. 2.7%), so detection bias likely doesn’t explain the entire gap. But it’s clear that official statistics undercount AFib in some communities more than others.
Many Cases Go Undiagnosed
A substantial number of people with AFib don’t know they have it. Estimates from a U.S. prevalence study found that about 11% of all AFib cases at any given point were undiagnosed. Over a two-year window, that figure rose to 23%, meaning nearly one in four people living with AFib hadn’t been identified.
The undiagnosed group tends to be older and, paradoxically, at higher risk for complications. Ninety-three percent of undiagnosed AFib patients in the study met clinical criteria for blood-thinning therapy to prevent stroke, but weren’t receiving it because no one knew they had the condition. AFib can be intermittent and sometimes causes no noticeable symptoms, which is why it often goes undetected until a routine exam or a complication like a stroke brings it to light.
Why the Numbers Matter: Stroke Risk
AFib isn’t just an irregular heartbeat. It’s one of the leading preventable causes of stroke. When the upper chambers of the heart quiver instead of contracting normally, blood can pool and form clots. If a clot travels to the brain, it causes a stroke. AFib is responsible for about 20% of all acute ischemic strokes, which are the type caused by a blocked blood vessel in the brain.
Strokes caused by AFib also tend to be more severe than strokes from other causes, which makes early detection and treatment especially important. This is the main reason that undiagnosed AFib is such a significant public health concern.
What Drives the Rising Numbers
The increase in AFib isn’t just about an aging population. Several modifiable risk factors are contributing to the trend. Obesity is one of the strongest. Research estimates a 4% increase in AFib risk for every one-point increase in BMI, and a five-point BMI increase accounts for roughly 30% of AFib cases. High blood pressure, diabetes, sleep apnea, and heavy alcohol use also raise risk substantially.
Better detection plays a role too. Smartwatches and portable heart monitors are identifying cases that would have gone unnoticed a decade ago. As screening technology becomes more widespread, the number of diagnosed cases will continue to climb, even beyond what population aging alone would predict.
Global Patterns
Worldwide, the countries with the highest absolute numbers of AFib cases are China, India, and the United States, largely because of their population sizes. When adjusted for age, high-income regions like North America, Australasia, and Western Europe have the highest rates. This likely reflects a combination of genuinely higher prevalence (driven by obesity, hypertension, and longer lifespans) and better detection infrastructure.
In 2021, AFib and the closely related condition atrial flutter caused an estimated 340,000 deaths globally and 4.48 million new cases were diagnosed that year alone. The burden falls disproportionately on wealthier nations in terms of raw case counts, but lower-middle-income countries bear a heavy toll in terms of disability and years of life lost, likely because access to treatment is more limited.