Does it matter which arm I use when I take my blood pressure?

Yes. In general you should take your blood pressure on your left arm. If you are unable to take your blood pressure on your left arm, you may take it on your right arm instead but you should be aware that there may be differences between your right and left arms. In some patients the differences can be as much as 10 mmHg or more. It is not recommended that you compare readings between both arms if you have taken multiple readings on both, as the results may vary due to the differences between the two arms.