Glossary term
Interest-Only ARM
An interest-only ARM is an adjustable-rate mortgage that lets the borrower pay only interest for an initial period before principal repayment begins.
Updated
Read time
What Is an Interest-Only ARM?
An interest-only ARM is an adjustable-rate mortgage that allows the borrower to make payments covering only interest for an initial period. During that time, the payment does not reduce the loan principal unless the borrower voluntarily pays extra.
After the interest-only period ends, the loan usually recasts into payments that include both principal and interest. Because the remaining principal must be repaid over a shorter remaining term, the payment can rise sharply, especially if the interest rate also adjusts upward.
Key Takeaways
- An interest-only ARM combines interest-only payments with adjustable-rate mortgage features.
- Early payments can be lower because they do not require principal repayment.
- The payment can increase when the interest-only period ends or when the rate adjusts.
- Borrowers should model the fully amortizing payment, not just the initial interest-only payment.
How an Interest-Only ARM Works
The loan starts with a period when scheduled payments cover only interest. The rate may be fixed for part of that period or may adjust according to the ARM terms. When the interest-only period ends, the lender recalculates the payment so the borrower repays principal and interest over the remaining loan term.
If the borrower made no principal payments during the interest-only period, the original balance may still be outstanding. That creates payment shock when amortization begins.
Payment Stages
Stage | Payment structure | Main risk |
|---|---|---|
Interest-only period | Scheduled payment covers interest only | Principal balance does not decline |
Rate adjustment | Rate may reset based on index plus margin | Payment may rise with rates |
Recast | Payment begins covering principal and interest | Monthly payment can jump |
Fully amortizing period | Loan must repay over remaining term | Less time remains to repay principal |
Borrower Review Points
An interest-only ARM can make early payments look manageable, but affordability should be tested against the later fully amortizing payment. Borrowers should ask when the interest-only period ends, when the rate can adjust, what caps apply, and what the maximum payment could be.
The structure may fit some sophisticated cash-flow situations, but it can be risky when a borrower depends on refinancing, selling, income growth, or home-price appreciation to handle the later payment.
It also slows equity building. If home prices are flat or fall, the borrower may have less cushion because scheduled payments did not reduce principal during the interest-only period.
The Bottom Line
An interest-only ARM lowers scheduled payments at first by delaying principal repayment, then can create a larger payment later. The key risk is not just the adjustable rate, but the combination of rate resets and a shortened principal repayment period.