Fixed-Rate vs Adjustable-Rate Mortgage — Which Is Right for You?
Fixed-rate mortgages give payment certainty; ARMs offer lower initial rates. See how to calculate the true cost of each option and when each makes sense.
Mortgage Calculator
Predictable payments for the life of the loan
What it measures: Monthly principal and interest payment on a fixed-rate loan — guaranteed not to change.
✓ Use when
- You plan to stay in the home for 7+ years
- You value payment predictability and budget stability
- You believe rates will rise over your holding period
- You are risk-averse and want to eliminate refinancing risk
✗ Limitations
- Higher initial rate than an ARM for the same loan amount
- If rates fall significantly, you must refinance to benefit
- Less flexibility than an ARM for short-term homeowners
Blended Rate Calculator
Track your true rate as your ARM adjusts over time
What it measures: The weighted average rate across multiple loans — useful for tracking blended cost as your ARM rate resets.
✓ Use when
- You have an ARM as one of several loans and want to track combined rate exposure
- Modeling blended cost under different ARM reset scenarios
- Comparing blended rate before and after an ARM resets
✗ Limitations
- Does not model future ARM adjustments automatically — you enter today's rate
Key difference
Fixed-rate mortgages are simple: one rate, forever. ARMs start lower but carry reset risk. The decision comes down to your expected holding period versus the initial rate discount.
Worked Example
Scenario
$400,000 loan. Fixed 30-year at 6.875%. 7/1 ARM at 5.875% (adjusts after 7 years, max +5% lifetime cap).
Fixed: $2,627/month, $546,000 total interest over 30 years
ARM: $2,366/month for 7 years ($1,530 savings/year) — then resets to unknown rate up to 10.875%
Interpretation
The ARM saves $10,710 over the fixed period. But if you stay past year 7 and rates rise, the ARM could cost far more. Break-even: the ARM wins if you sell or refinance within ~7 years.
Bottom line
ARMs make sense if you are confident you will move or refinance within the fixed period. For long-term homeowners, the payment certainty of a fixed rate is usually worth the premium.