Which arm usually reads higher?

Neither arm is always higher across everyone. In a 2026 Shanghai study the right arm read higher, but the right arm was always measured first. Your own higher arm is the one that reads higher on repeat checks.

Is a 20 mmHg difference between arms dangerous?

A repeat 20 mmHg gap is well above the 10 and 15 mmHg cutoffs used by guidelines. It does not prove a blockage, but it is a reason to see your clinician soon. They may check the pulses in your arms and legs or order an ultrasound.

Which arm should I use for my daily readings?

Use the arm that gave the higher reading on your two-arm checks. Guidelines from the ESC and NICE both say to use the higher arm. Using the lower arm can make your blood pressure look better than it is.

Can a big arm difference go away?

Many large gaps found on a single check disappear when readings are repeated, because they came from timing or technique. A gap caused by a narrowed artery tends to stay. Repeat the test on another day before you draw conclusions.

Does a difference in diastolic pressure matter?

Most research and guideline cutoffs use the systolic (top) number. Diastolic gaps also occur, with a mean of about 3.6 mmHg in one meta-analysis. Report both numbers to your clinician, but the systolic gap is the one guidelines act on.

Why Is Blood Pressure Different in Each Arm?

The short answer: A small gap between arms is normal. Most people differ by about 5 mmHg systolic, per a 2011 meta-analysis. The 2024 ESC guideline treats a systolic gap above 10 mmHg as an inter-arm difference. A gap that size can point to narrowed arteries, so measure both arms and use the higher one.

How much difference between arms is normal?

Your two arms rarely read the same. A 2011 meta-analysis in the American Journal of Hypertension found a mean absolute difference of 5.4 mmHg systolic and 3.6 mmHg diastolic. In that pooled data, 14% of people had a systolic gap of 10 mmHg or more, and 4% had 20 mmHg or more.

How common a large gap is depends on who is measured and how. A 2016 review of studies that measured both arms at the same time found a systolic gap of 10 mmHg or more in:

3.6% of general adult populations
7.4% of people with diabetes
11.2% of people with hypertension

So a difference of a few points is expected. A difference of 10 mmHg or more that repeats is less common and worth a closer look.

What difference do guidelines call significant?

Guidelines agree on the method but use different cutoffs:

Europe (2024 ESC): The guideline says to measure both arms at the first visit. It defines an inter-arm difference as a systolic gap of more than 10 mmHg. If you have one, later readings use the arm with the higher value.
England (NICE NG136): NICE uses 15 mmHg. If the gap is more than 15 mmHg, repeat the readings. If it stays above 15 mmHg, use the higher arm from then on.
United States: The 2025 AHA/ACC guideline replaced the 2017 ACC/AHA guideline. The 2022 INTERPRESS-IPD paper notes that guidelines recommend measuring both arms and using the higher arm's readings.

Researchers lean toward the lower cutoff. The INTERPRESS-IPD collaboration pooled 24 studies and proposed 10 mmHg systolic as the upper limit of normal.

What causes a big difference between arms?

A large, repeatable gap usually means blood flow into one arm is reduced. The arm with less flow reads lower. The main causes are:

Subclavian artery stenosis. The subclavian artery feeds each arm. Plaque can narrow it. In angiography studies in the 2012 Lancet meta-analysis, people with a proven narrowing of more than 50% had a mean gap of 36.9 mmHg. A gap of 10 mmHg or more made subclavian stenosis 8.8 times more likely.
Peripheral artery disease. NHLBI explains that PAD is plaque buildup that reduces blood flow in arteries outside the heart. It can affect the legs, arms, or pelvis. More than 8 million US adults aged 40 and older have it.
Coarctation of the aorta. This is a narrowing of the main artery, present from birth. MedlinePlus notes it is 5% to 7% of congenital heart defects. Blood pressure in the legs is usually lower than in the arms. The ESC guideline lists it as a cause of an arm gap that may need tests.
Measurement error. This is a common reason for a false gap. Blood pressure changes from minute to minute. If you measure one arm and then the other, part of the gap is just time passing.

To find a narrowing, doctors may use ultrasound, CT, or MR angiography. MedlinePlus lists MR angiography as one test for coarctation. Our sister site mri.md explains how MRI scans work.

Does a difference between arms raise heart risk?

Yes, on average. The gap is a marker of artery disease, not a disease on its own. The 2012 Lancet meta-analysis by Clark and colleagues pooled 20 studies. A gap of 15 mmHg or more was linked to:

2.5 times the risk of peripheral vascular disease
1.6 times the risk of prior stroke or other cerebrovascular disease
a 1.7 hazard ratio for cardiovascular death
a 1.6 hazard ratio for death from any cause

The larger INTERPRESS-IPD analysis used data on 53,827 people. Each 5 mmHg of systolic gap raised the risk of death from any cause by about 5%. It raised cardiovascular death risk by about 6%. The risk stayed after adjustment for standard heart risk scores.

A follow-up INTERPRESS-IPD study looked at 53,172 people. Using the higher arm instead of the lower arm moved 12% of them across the 130 or 140 mmHg systolic thresholds. In other words, reading only the lower arm can miss high blood pressure.

Should you measure both arms at once or one after the other?

At the same time is more accurate. One after the other is more practical. The 2016 review found that sequential readings overestimate how often a 10 mmHg gap occurs by about three times. The 2011 meta-analysis found the same direction of error. Sequential, manual, and single readings each about doubled the chance of a false 10 mmHg gap.

Order matters too. A 2026 study of 7,838 people in Shanghai measured the right arm first, then the left. The right arm read higher again and again, which suggests the first arm gets a small boost.

The ESC guideline still accepts sequential readings as reliable enough. The fix is simple: take several readings and switch the order.

How do you check both arms at home?

This checklist follows the methods in the studies above. Use an automated upper-arm monitor. See our guide to home blood pressure monitoring for cuff size and posture.

Sit quietly and rest first, with your back supported and feet flat. Rest both arms at heart level.
If you have two identical automated monitors, put one cuff on each arm and start both at the same time. This is the most accurate method.
If you have one monitor, measure the right arm, then the left arm, about 1 minute apart.
Take a second round in the opposite order: left arm first, then right. This cancels out the first-arm effect.
Average the systolic numbers for each arm. Subtract the lower average from the higher one.
If the gap is 10 mmHg or more, repeat the whole set on another day. One high gap is often error.
If the gap repeats, use the higher arm for all future home readings. Write down which arm it is.
Bring your log to your clinician, with both arms and the dates. A repeat gap of 10 to 15 mmHg or more is a reason to ask about artery checks.

Tell your clinician soon if a gap comes with muscle pain or weakness in that arm during activity. NHLBI describes that pattern in the legs as a sign of PAD, and the same reduced flow can affect an arm.

A gap between arms is a different issue from readings that jump around over the day. That is covered in why blood pressure varies between readings.

The bottom line

A few points of difference between arms is normal. A repeat systolic gap above 10 mmHg (ESC) or 15 mmHg (NICE) is significant. It can signal narrowed arteries and higher heart risk. Measure both arms, take more than one round, and use the higher arm. Show a repeat gap to your clinician.

Last updated: October 2026. This article is for informational purposes only and does not constitute medical advice. Talk to your clinician about any repeat difference between your arm readings.