You can take blood pressure on either arm, but the readings may not be identical. Most people have a small, harmless difference between arms, averaging about 1 mmHg for systolic pressure. Major guidelines from the U.S., Europe, and the U.K. all recommend measuring both arms at your first blood pressure assessment, then using the arm with the higher reading for all future measurements.
Why Both Arms Matter at Your First Check
The American College of Cardiology guidelines tell clinicians to verify that the difference between your left and right arms is insignificant. The European Society of Cardiology and UK NICE guidelines echo this, recommending a two-arm check when you’re first being evaluated for high blood pressure. If there is a meaningful gap, every reading after that should come from whichever arm gave the higher number. Using the lower arm by habit could mask hypertension and lead to undertreatment.
In practice, many clinics skip this step. If you’ve never had your blood pressure compared across both arms, it’s worth asking at your next visit.
What’s a Normal Difference Between Arms
A study measuring inter-arm differences found the average systolic gap between right and left was just 1.1 mmHg, with a normal range spanning roughly 10 mmHg in either direction. For diastolic pressure, the average difference was essentially zero. These gaps don’t correlate with age or baseline blood pressure level, so having a small difference is common regardless of how old you are or whether your pressure runs high.
A difference under 10 mmHg systolic is generally considered normal and doesn’t change how your blood pressure should be managed.
When a Larger Gap Is a Warning Sign
A systolic difference of 10 mmHg or more between arms starts to carry clinical significance. In one large cohort, about 11% of participants had a gap that size. Among people with hypertension, a difference of 10 mmHg or greater was linked to nearly triple the risk of dying from cardiovascular causes compared to those with smaller gaps. Even a persistent difference of 5 mmHg or more has been associated with roughly 1.9 times the risk of cardiovascular death in people already at elevated heart risk.
A gap of 15 mmHg or more is considered suggestive of arterial disease, particularly narrowing of the subclavian artery, which supplies blood to the arm. Only about 3% of people have a difference this large, but it flags meaningfully higher cardiovascular risk and typically prompts further evaluation. In that same research, about 9% of people with a 10 mmHg gap were reclassified into a higher 10-year heart disease risk category once the higher arm reading was used, meaning the difference was large enough to change treatment decisions.
What Causes the Difference
Small differences are simply normal variation. Larger, persistent gaps point to problems with blood flow on one side. The most common culprit is subclavian artery stenosis, a narrowing of the artery that feeds the arm. Other potential causes include aortic aneurysm, aortic coarctation (a congenital narrowing of the aorta), inflammation of blood vessels, and compression of blood vessels near the collarbone. These conditions restrict flow to one arm, producing a lower reading on that side.
Because the lower-reading arm is the one with reduced blood flow, it gives a falsely reassuring number. That’s the core reason guidelines say to use the higher arm going forward.
Simultaneous vs. One Arm at a Time
If your clinician checks both arms one after the other (sequential measurement), natural fluctuations in blood pressure between readings can inflate the apparent difference. Research comparing the two approaches found that sequential measurements produced an average systolic gap of 7.8 mmHg, while simultaneous measurement (cuffs on both arms at once) gave a gap of only 6.2 mmHg. Clinically relevant gaps of 10 mmHg or more appeared in 26% of people measured sequentially but only 18% measured simultaneously.
Simultaneous measurement is more accurate for identifying a true inter-arm difference because it eliminates the effect of your blood pressure naturally drifting between one reading and the next. Not every clinic has dual-arm equipment, but if you’re being checked specifically for an inter-arm difference, simultaneous measurement is the preferred method.
When One Arm Should Be Avoided
There are situations where blood pressure should not be taken on a particular arm. After a mastectomy or lymph node removal, the arm on the surgical side is typically off-limits for blood pressure cuffs, blood draws, and IV placement because compression can worsen swelling or trigger lymphedema. The same applies if you have a dialysis fistula or graft in one arm: the cuff can damage the access site.
If both arms are restricted (for example, bilateral mastectomy or other surgical history on both sides), clinicians can sometimes use a forearm or leg cuff. In breast cancer patients, current evidence suggests the surgical-side arm can be used if the opposite arm is unavailable, as long as there is no active lymphedema, blood clot, or central catheter in place.
Getting the Most Accurate Reading
Whichever arm you use, technique matters more than arm choice for day-to-day accuracy. The cuff’s midpoint should sit at heart level, with your arm supported on a table or desk. Your back should be supported, feet flat on the floor, and legs uncrossed. A 2024 randomized trial found that simply resting your arm in your lap instead of on a desk produced meaningfully different readings, even when every other measurement step was done correctly. If you monitor at home, use the same arm every time (the one your clinician identified as the higher-reading arm) and keep your positioning consistent.