Fixed vs Adjustable Rate Mortgage: How They Compare & Which to Choose
Side-by-Side Comparison
| Feature | Fixed-Rate Mortgage | Adjustable-Rate Mortgage (ARM) |
|---|---|---|
| Interest rate | Locked for entire term | Fixed for initial period, then adjusts annually |
| Initial rate | Higher than ARM’s initial rate | 0.5–1.5% lower than equivalent fixed |
| Monthly payment | Never changes (P&I portion) | Can increase significantly after initial period |
| Payment predictability | Complete certainty | Uncertain after initial fixed period |
| Rate risk | None — you’re protected from rising rates | High — payments can increase substantially |
| Common terms | 15-year, 30-year | 5/1, 7/1, 10/1 ARM |
| Best for | Long-term homeowners, risk-averse buyers | Short-term owners, high-rate environments |
How Fixed-Rate Mortgages Work
A fixed-rate mortgage is straightforward: you lock in a rate at closing, and it stays that rate for the entire loan term. On a 30-year fixed at 7%, your principal and interest payment on a $300,000 loan is $1,996/month — forever. Property taxes and insurance may change, but the mortgage itself is predictable.
The 30-year fixed is the most popular mortgage in America (~90% of purchase loans) for good reason: payment certainty makes budgeting easy and eliminates interest rate risk. The 15-year fixed offers lower rates (typically 0.5–0.75% less) and saves massive interest, but payments are ~40% higher.
How Adjustable-Rate Mortgages Work
ARM notation tells you the structure. A “5/1 ARM” means the rate is fixed for 5 years, then adjusts once per year. A “7/6 ARM” is fixed for 7 years, then adjusts every 6 months. The initial fixed period is your window of savings.
After the fixed period, your rate adjusts based on an index (typically SOFR — Secured Overnight Financing Rate) plus a margin (typically 2–3%). Rate caps limit how much your rate can change per adjustment (usually 2%) and over the loan’s lifetime (usually 5–6% above the initial rate).
| ARM Type | Fixed Period | Adjustment Frequency | Best For |
|---|---|---|---|
| 5/1 ARM | 5 years | Annual | Selling or refinancing within 5 years |
| 7/1 ARM | 7 years | Annual | Moderate time horizon, confident you’ll move or refi |
| 10/1 ARM | 10 years | Annual | Longer stay but want initial savings |
| 5/6 ARM | 5 years | Every 6 months | Similar to 5/1 but more frequent adjustments |
The Math: When ARMs Save Money
Let’s compare a $400,000 loan at current rates. Assume a 30-year fixed at 7.0% vs a 7/1 ARM at 6.0%:
| Metric | 30-Year Fixed (7.0%) | 7/1 ARM (6.0% initial) |
|---|---|---|
| Monthly P&I | $2,661 | $2,398 |
| Monthly savings with ARM | — | $263/month |
| Total savings over 7 years | — | ~$22,000 |
| After year 7 | Still $2,661 | Adjusts — could rise to $3,000+ depending on rates |
If you sell or refinance within the ARM’s fixed period, you pocket the savings with zero risk. The danger is if you’re still in the loan when adjustments begin and rates have risen significantly.
When to Choose a Fixed-Rate Mortgage
Choose fixed if you plan to stay in the home long-term (7+ years), want payment certainty for budgeting, are risk-averse, or rates are historically low and worth locking in. The peace of mind of knowing your payment will never increase is valuable — especially for first-time buyers adjusting to homeownership costs.
When to Choose an ARM
Choose an ARM if you’re confident you’ll sell or refinance before the adjustment period, current fixed rates are high and you expect rates to fall (allowing a future refinance), you’re disciplined enough to invest the monthly savings, or you’re buying a starter home you’ll outgrow.
Key Takeaways
- A 30-year fixed is the safest choice for long-term homeowners — your payment never changes.
- ARMs save 0.5–1.5% on the initial rate, which can mean $200–$400/month on a typical loan.
- Only choose an ARM if you’ll sell or refinance before the adjustment period — or can handle worst-case payments.
- Rate caps (2% per adjustment, 5–6% lifetime) limit your worst case, but that’s still a significant payment increase.
- Never use an ARM to stretch into a more expensive home — if you need the lower rate to qualify, the house is too expensive.
Frequently Asked Questions
What does 5/1 ARM mean?
The first number (5) is the initial fixed-rate period in years. The second number (1) is how often the rate adjusts after the fixed period. A 5/1 ARM has a fixed rate for 5 years, then adjusts once per year. A 5/6 ARM adjusts every 6 months after the initial period.
Can my ARM rate go down?
Yes. If the underlying index rate falls, your ARM rate can decrease. However, ARMs have a floor (minimum rate) that’s usually equal to the margin. Historically, the risk is more to the upside — most people get ARMs when rates are already low, meaning there’s more room for rates to rise than fall.
Can I refinance from an ARM to a fixed rate?
Yes, and this is a common strategy. Many borrowers take an ARM for the initial savings and plan to refinance to a fixed rate before the adjustment period. The risk is if rates rise significantly or your home value drops (reducing your equity), making refinancing less favorable or harder to qualify for.
What happens if I can’t refinance before my ARM adjusts?
Your rate adjusts according to the loan terms — index rate + margin, subject to the cap structure. On a 5/1 ARM with a 2/2/5 cap structure, the rate can increase up to 2% at the first adjustment, 2% at each subsequent adjustment, and no more than 5% over the initial rate lifetime. A 6% initial rate could theoretically reach 11% — which would increase payments dramatically.
Are ARMs as risky as they were before 2008?
No. Post-crisis regulations eliminated the worst ARM products (negative amortization, interest-only, no-doc loans). Today’s ARMs require full documentation, have reasonable cap structures, and must be underwritten at a qualifying rate higher than the initial rate. They’re legitimate products for the right borrower — but still carry interest rate risk.