Margin (ARM)
Direct definition
The fixed spread added to an ARM's index to determine the fully indexed interest rate.
Written by the Vabasso Mortgage Editorial Team · Reviewed against agency and federal sources · Read our editorial policy for how we research and review mortgage content
Plain-English explanation
The margin doesn't change over the loan's life. At each adjustment, the new rate equals index plus margin, subject to caps.
Why it matters
A lower margin means a lower rate at every future adjustment.
Where you may see it
- ARM disclosure
- Note
- Adjustable-rate rider
- Rate change notice
A real-world example
With an index of 4.75% and a margin of 2.5%, the fully indexed rate is 7.25%.
Educational and illustrative only
A common misunderstanding
The margin doesn't change over the life of the loan — only the index does. It's not the same thing as the fully indexed rate itself.
Ask Vabasso AI
This glossary provides general educational information. Mortgage terminology, qualification methods, forms, timelines, fees, program rules, and legal meanings may vary by lender, investor, loan program, property, occupancy, state, and transaction. Definitions do not represent loan approval, legal advice, tax advice, or a commitment to lend.
- Author
- Vabasso Mortgage Editorial Team
- Reviewed by
- Vabasso Mortgage Licensed Advisory Team
- Last reviewed
- July 30, 2026