Which Blood Type Is Most Common? Comparison Guide

Blood type O positive is the most common blood type in the United States. About 37% of the U.S. population has O positive blood. If you add O negative, nearly half of all Americans have type O blood. The next most common is A positive at roughly 28%. These numbers come from the American Red Cross and have held steady for decades. Your blood type depends on genetics and varies by ethnicity, but globally O positive remains the most frequent.

What Are the Different Blood Types and How Common Is Each One?

Blood types are determined by two systems: the ABO group and the Rh factor. The ABO system gives you type A, B, AB, or O. The Rh factor tells you whether you are positive or negative. That makes eight possible blood types.

Here is the breakdown for the U.S. population based on data from the American Red Cross:

O positive is the most common because it is the oldest blood type evolutionarily. Type O emerged before humans migrated out of Africa. Type A and B came later through genetic mutations. AB is the newest and rarest, appearing only about 1,000 years ago.

Does Blood Type Distribution Vary by Race and Ethnicity?

Yes, blood type frequencies shift depending on ancestry. The numbers above are averages for the whole U.S. population. When you look at specific groups, the picture changes.

According to the Red Cross, here is how O positive breaks down by ethnicity in the U.S.:

• Hispanic: about 53% have O positive
• African American: about 47% have O positive
• Asian: about 39% have O positive
• Caucasian: about 37% have O positive

Blood type B is more common in Asian populations than in Caucasians. About 25% of people in China have type B, compared to roughly 9% of white Americans. AB is rare everywhere, but slightly more common in Japanese and Korean populations. These differences matter for blood donation matching and for understanding disease risk in different groups.

Which Blood Type Is Most Common Globally?

O positive is also the most common blood type worldwide. Estimates from the World Health Organization suggest about 40% of the global population has type O positive. Type A positive is next at roughly 28% globally.

But there are regional differences. In some parts of Central and South America, O positive reaches 60% or higher. In Norway and Sweden, type A positive is nearly as common as O positive. Type B is more frequent in northern India and Central Asia. Type AB never exceeds 10% in any population studied.

The global rarity of AB negative is why blood banks often struggle to keep it in stock. Only about 1% of people worldwide have AB negative blood. If you have it, your donation is especially valuable for plasma and platelet transfusions.

What Does Research Say About Blood Type and Health Risks?

Some studies suggest your blood type may influence your risk for certain health conditions. The evidence is strongest for heart disease and stomach issues. But the research is not settled, and the risk differences are small for most people.

Research published in the journal Arteriosclerosis, Thrombosis, and Vascular Biology found that people with type O blood have a lower risk of heart attack and stroke. Those with type A, B, or AB had a 9% higher risk of cardiovascular events. The reason may involve blood clotting. People with non-O blood types have higher levels of von Willebrand factor, a protein that helps blood clot.

Studies have also found that people with type O blood are less likely to develop blood clots in veins, known as deep vein thrombosis. The American Heart Association has reported that type O blood carries about half the clotting risk of other types.

On the other hand, type O blood may increase your risk for stomach ulcers caused by H. pylori bacteria. Some studies suggest type O blood makes it easier for this bacteria to attach to stomach cells. This is a real finding but the absolute risk increase is modest.

There is no strong evidence that blood type determines your personality, your ideal diet, or your likelihood of getting cancer. Those claims have been widely shared online but lack solid clinical backing. The blood type diet, for example, has been tested in clinical trials and found to have no meaningful effect on health independent of other factors.

Can You Change Your Blood Type?

No, your blood type is fixed from birth. It is determined by the genes you inherit from your parents. You cannot change it through diet, exercise, or any medical procedure.

There is one rare exception. A bone marrow transplant can change a person’s blood type. This happens because the transplanted marrow produces new blood cells with the donor’s blood type. The recipient’s blood type gradually shifts to match the donor’s. This is a known effect in transplant medicine and is not something that happens outside of that specific treatment.

Some viral health claims suggest that certain foods or supplements can “convert” your blood type. As of 2026, there is no clinical evidence that any food, herb, or supplement can change your blood type. These claims are false and should be ignored.

What Should You Know About Blood Donation and Your Blood Type?

Blood banks always need donations from all types. But some types are more urgently needed than others. O negative is the universal donor for red blood cells. It can be given to anyone in an emergency when the patient’s blood type is unknown. Only about 7% of people have O negative, so it is always in short supply.

O positive can be given to anyone with a positive Rh factor. That covers about 85% of the population. AB positive is the universal recipient for red blood cells. People with AB positive can receive any type of blood. AB plasma is also universal, meaning it can be given to any patient regardless of blood type.

If you want to donate, knowing your blood type helps the blood bank match you to the most urgent need. You can find out your blood type through a simple test at a donation center or through a blood type test kit. Many blood drives also offer free blood type testing when you donate.