ARM vs Fixed Rate Mortgage Calculator
Compare adjustable and fixed-rate mortgages year by year to find which option saves more over your time horizon.
For educational purposes only. Calculator results are estimates based on the inputs you provide and are not a substitute for professional financial advice. Consult a licensed financial advisor before making investment, borrowing, or retirement decisions.
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Fixed rate vs adjustable rate mortgages
A fixed-rate mortgage locks in the same interest rate for the entire loan term. Your payment never changes — offering predictability and protection against rate increases. A fixed rate is ideal if you plan to stay in the home long-term or if current rates are historically low.
An adjustable-rate mortgage (ARM) starts with a lower fixed rate for an initial period (typically 3, 5, 7, or 10 years), then adjusts annually based on a market index. ARMs are expressed as 5/1, 7/1, etc. — the first number is the initial fixed period in years, the second is how often it adjusts thereafter. ARMs can save money if you plan to move or refinance before the adjustment period begins.
How to use this calculator
- Loan Amount — The total amount you are borrowing.
- Fixed Interest Rate — The rate on the fixed-rate option you are comparing.
- ARM Initial Rate — The starting rate during the ARM's fixed period (usually lower than the fixed-rate option).
- ARM Fixed Period — How long the initial ARM rate holds before adjustments begin.
- Rate Caps — The maximum annual and lifetime rate increases allowed on the ARM.
- Click Calculate to see the year-by-year payment and cumulative interest comparison.
Understanding ARM rate caps
ARMs include protections to limit how much your rate can rise:
- Initial cap — Maximum rate increase at the first adjustment (often 2–5%)
- Periodic cap — Maximum rate increase at each subsequent adjustment (typically 1–2%)
- Lifetime cap — Maximum total rate increase over the life of the loan (typically 5–6% above the initial rate)
Frequently asked questions
When does an ARM make financial sense?
An ARM is advantageous when you plan to sell or refinance before the fixed period ends, when current fixed rates are unusually high, or when the initial savings are substantial and you can absorb potential future increases.
What index do ARMs typically track?
Most modern US ARMs are indexed to SOFR (Secured Overnight Financing Rate), which replaced LIBOR in 2023. Your rate is the index plus a fixed margin set by the lender.
What happens if I cannot afford my ARM payment after it adjusts?
If your ARM adjusts upward significantly and the payment becomes unaffordable, you have three main options: (1) refinance into a fixed-rate mortgage before or during the adjustment period — this is the most common strategy; (2) make extra principal payments during the fixed period to reduce the loan balance before adjustments begin; (3) sell the property if you have sufficient equity. The risk is highest when rates rise broadly — exactly when refinancing into a fixed rate also becomes expensive. Always stress-test your budget against the lifetime cap before choosing an ARM.
ARM or Fixed Rate — Which Is Right For You?
| Your Situation | Best Choice | Reason |
|---|---|---|
| Staying in the home 10+ years | Fixed Rate | Certainty outweighs initial savings |
| Moving or selling within 5–7 years | ARM (5/1 or 7/1) | Exit before rate adjustments begin |
| Mortgage rates are historically high | ARM | Position to benefit from future rate drops |
| Mortgage rates are historically low | Fixed Rate | Lock in before rates rise |
| Variable income or tight monthly budget | Fixed Rate | Payment certainty protects cash flow |
| Strong savings buffer (6+ months expenses) | ARM | Can absorb worst-case rate adjustments |
| Likely to refinance within 5 years | ARM | Will never reach the adjustable period |
Not sure which applies to you? Use the calculator above to model both scenarios with your exact loan numbers.
ARM vs fixed rate in real scenarios
5/1 ARM at 5.5% vs 30-year fixed at 6.5% on a $400,000 loan
With a 5/1 ARM at 5.5%, your monthly payment is $2,271 vs $2,528 for a 30-year fixed at 6.5% — a difference of $257/month. Over 5 years, you save $15,420 with the ARM. If you sell or refinance before year 6, the ARM wins outright. If the rate adjusts to 8% in year 6, your payment jumps to $2,817 and the fixed-rate option becomes cheaper within 3 years.
What if ARM rates rise 2% after the fixed period?
A $350,000 5/1 ARM starting at 5.25% adjusts to 7.25% in year 6 after a 2% rise. Your payment goes from $1,932 to $2,340 — an increase of $408/month. If it hits the lifetime cap (say 10.25%), the payment reaches $2,817. Many borrowers underestimate this adjustment risk; stress-test your budget against the lifetime cap before choosing an ARM.
Planning to move in 7 years — does the ARM make sense?
A 7/1 ARM at 5.75% on a $400,000 mortgage costs $2,334/month. A 30-year fixed at 6.75% costs $2,594/month. Over 7 years, the ARM saves $21,840. If you move at year 7 as planned, the ARM delivers clear savings with minimal risk. The risk materialises only if plans change and you stay beyond year 7 into the adjustable period — which happens more often than buyers expect.