You should check blood pressure in both arms the first time, then use the arm that gives the higher reading for all future measurements. A small difference between arms is normal, but consistently using the higher-reading arm ensures you’re tracking the number that matters most for your health.
Why Both Arms Matter at First
Most people assume it doesn’t matter which arm they use, but blood pressure can differ between your left and right arms. The difference is often small, just a few points, and it’s completely normal. Slight variations in artery size, the angle at which blood vessels branch off the aorta, and differences in muscle mass all contribute.
The important step is checking both arms at least once, ideally during your first time monitoring at home or at your first clinic visit. Once you know which arm reads higher, that becomes your measurement arm going forward. This gives you the most accurate picture of your cardiovascular risk, because underestimating your blood pressure by always using the lower arm could mean missing a diagnosis of high blood pressure.
When the Difference Between Arms Is a Warning Sign
A difference of 10 mmHg or more between arms, especially in the systolic (top) number, is worth paying attention to. Research published in the American Heart Association’s journal Hypertension found that a systolic interarm difference is associated with increased all-cause mortality, cardiovascular mortality, and cardiovascular events. People with larger differences also tend to have greater arterial stiffness and increased heart muscle mass.
Cross-sectional studies have found that significant interarm differences show up more often in people who already have diabetes, cardiovascular disease, cerebrovascular disease, or peripheral arterial disease. That doesn’t mean a difference causes these conditions, but it can be an early signal that blood vessels on one side are narrower or stiffer than the other. If you notice a consistent gap of 10 points or more between your arms, it’s worth bringing up at your next appointment.
How to Get an Accurate Reading
Which arm you choose only matters if the reading itself is reliable. Poor technique can swing your numbers by 10 to 20 points in either direction, which is enough to mask high blood pressure or create a false alarm.
Start with your position. Sit in a chair that supports your back, feet flat on the floor, legs uncrossed. Rest your upper arm on a table so it’s level with your heart, palm facing up, muscles relaxed. If your arm hangs at your side or sits below heart level, blood pools and artificially raises the reading. If it’s too high, the reading drops.
Place the cuff on your bare upper arm, about one inch above the bend of your elbow. Putting it over clothing, even a thin sleeve, can add several points to your result. The cuff should be snug but not tight: you should be able to slide one finger underneath.
Don’t talk during the measurement. Conversation alone can raise systolic pressure by 10 or more points. Sit quietly for at least five minutes before you start, and take two readings at least one minute apart. Use the average of those two readings as your number for that session.
Staying Consistent With Home Monitoring
Once you’ve identified your higher-reading arm, stick with it every time. Switching between arms from day to day introduces variability that makes it harder to spot real trends. The whole point of home monitoring is tracking changes over time, and consistency is what makes those trends visible.
The American Heart Association recommends taking two readings in the morning and two in the evening over the course of a week when establishing a baseline or diagnosing high blood pressure. After that initial period, your doctor can advise how often to continue checking. Many people with well-controlled blood pressure settle into a routine of a few times per week.
Record every reading with the date, time, and which arm you used. Most automatic monitors store results, but keeping a written or app-based log makes it easier to share with your doctor and spot patterns related to medications, stress, or diet changes.
Left Arm vs. Right Arm: Does One Default?
There is no universal rule that one arm is always better. You may have heard that the left arm is preferred because it’s closer to the heart, but in practice the anatomical difference is minimal and doesn’t reliably predict which arm will read higher. Some people consistently read higher on the right, others on the left. The only way to know is to measure both.
If you’ve never checked both arms and you need to pick one right now, using your non-dominant arm is a reasonable starting point simply because it’s easier to operate the monitor with your dominant hand. But treat that as a temporary choice until you can compare both sides.