A fixed-rate mortgage keeps its note rate unchanged for the term; an adjustable-rate mortgage (ARM) can change after its initial fixed period under its index, margin, and caps. A 5/1 ARM can begin with a lower payment yet become materially more expensive when the first adjustment arrives.
fixed rate vs adjustable rate mortgage: the measured relationship
A fixed-rate mortgage has a rate set for the loan term, while an ARM has an initial fixed-rate period followed by contract-defined adjustments. A 15-year versus 30-year choice changes the repayment term. This choice changes whether the rate itself can move after closing.
| Original balance | $300,000 |
|---|---|
| Initial rate | 5.50% per year |
| First-reset cap | 2 percentage points |
| Illustrated reset | 7.50% per year |
| Illustrated payment change | about $514 per month |
fixed rate vs adjustable rate mortgage: a worked dollar case
On a $300,000 balance amortized over 30 years, 5.50% produces about $1,703 principal and interest each month. If a 5/1 ARM's first adjustment cap is 2 percentage points, its 5.50% rate could be as high as 7.50% at the first reset. With 25 years remaining, 7.50% produces about $2,217 per month, about $514 more; the contract sets the real outcome.
fixed rate vs adjustable rate mortgage: calculation method
For an ARM reset, fully indexed rate equals the named index plus fixed lender margin, then the note's periodic and lifetime caps apply. Recalculate from the remaining balance and remaining term, not the original balance.
fixedratevsadjus related calculations: fixed-payment scenario; remaining balance schedule; monthly payment comparison.
Common mistakes in Fixed-rate vs. adjustable-rate mortgage: what risk are you taking?
Do not call a 5/1 ARM a five-year loan, or use the introductory rate as a lifetime rate. Check adjustment timing, index, margin, floor, and caps in the disclosure.
Where this calculation stops
This illustration does not predict the index, property taxes, insurance, refinance availability, or income. Payment caps and negative-amortization features differ by contract.
fixed rate vs adjustable rate mortgage: source check
The Consumer Financial Protection Bureau explains that an ARM's post-introductory rate is index plus margin subject to caps, and advises checking how high the payment can go. Read the named source. The fixedratevsadjus record should be reconciled to the disclosure, statement, tax bill, or agreement that governs that exact transaction.
fixed rate vs adjustable rate mortgage: using the output
The fixedratevsadjus output keeps each input's named unit and date adjacent to the result. Update the fixedratevsadjus scenario when its rate, balance, payment, or property value changes.