The amount of the margin can differ from one lender to another, but it is usually constant over the life of the loan. Let's say, for example, that you are comparing ARMs offered by two different lenders. Both lenders use the one-year Treasury index. Here is how that difference in margin would affect your initial monthly payment. In comparing ARMs, look at both the index and margin for each plan.
Some indexes have higher average values, but they are usually used with lower margins.
Be sure to discuss the margin with your lender. When Banks Compete.