It’s quite common for blood pressure to vary from one arm to another. Typically, the pressure is a little higher in the dominant arm; for example, right-handed people will have higher readings in their right arms. According to the American Heart Association, if the difference between your two arms is 10 millimeters of mercury or less - typically written as 10 mm Hg - you are within the normal range, and there’s no cause for concern. If your pressure is indeed usually slightly higher in one arm, use that arm consistently for blood pressure checks. However, if there’s a difference of more than 20 mm Hg for systolic pressure (the top number in a blood pressure reading) or more than 10 mm Hg for diastolic pressure (the bottom number) between arms, that could indicate a problem - such as narrowing of the high-pressure arm’s main artery. If you discover such a difference while taking blood pressure at home, tell your physician, who may refer you for more tests.