Mortgage Margin
A mortgage margin is the fixed percentage a direct lender adds to an index (such as SOFR or the 1-year Treasury) to calculate the interest rate on an adjustable-rate mortgage (ARM). The margin is set at loan origination and does not change for the life of the loan. It is the direct lender's built-in profit spread on an ARM product, similar to a fixed markup on a variable-price input.
ARM pricing works in two parts: the index (a market-determined rate that fluctuates) plus the margin (a fixed spread set by the direct lender). For example, if a direct lender sets a 2.75% margin on a SOFR ARM and SOFR is currently at 5.30%, the fully-indexed rate is 8.05% — but caps on the loan may mean the actual rate adjusts more gradually. The margin is disclosed on your Loan Estimate and Note and cannot change.
Direct lenders compete on margin as well as initial rate. Two lenders might both offer a 5/1 SOFR ARM with a 6.875% initial rate, but one might have a 2.50% margin and the other a 2.75% margin. The lower-margin product from the direct lender with the 2.50% spread will perform better for the borrower if SOFR rises, because each adjustment is calculated off the lower base. After the fixed period ends, margin matters more than initial rate.
Common ARM indexes include SOFR (now the dominant index after LIBOR retirement), the 1-year Constant Maturity Treasury (CMT), and the 11th District Cost of Funds Index (COFI). Each direct lender chooses which index to reference; most have standardized on SOFR since 2023. When comparing ARM quotes from multiple direct lenders, always compare the margin and caps alongside the initial rate — the cheapest initial rate with the highest margin may cost more over time.
Key Takeaway
A mortgage margin is the fixed percentage a direct lender adds to an index (such as SOFR or the 1-year Treasury) to calculate the interest rate on an adjustable-rate mortgage (ARM). The margin is set at loan origination and does not change for the life of the loan. It is the direct lender's built-in profit spread on an ARM product, similar to a fixed markup on a variable-price input.
Related Terms
Frequently Asked Questions
Most direct lenders price ARM margins between 2.25% and 3.00% for conventional loans. Non-QM and jumbo ARMs may carry margins of 3.00%–4.00%. The lower the margin, the better the loan performs for the borrower over time.
No. The margin is fixed at loan origination and cannot change for the life of the loan, regardless of market conditions. Only the index portion of your ARM rate changes at each adjustment.
The margin directly determines your rate after the initial fixed period. A 2.50% margin on a 5/1 ARM means that if SOFR is at 5.00% after five years, your rate adjusts to 7.50%. Compare margins across direct lenders when shopping ARMs.
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