Calculate ARM payments through the intro period and after each rate adjustment. See potential payment shock and compare total cost vs a fixed-rate mortgage.
An adjustable-rate mortgage (ARM) offers a lower initial interest rate for a fixed introductory period — typically 3, 5, 7, or 10 years — then adjusts periodically based on a market index plus a lender margin. This can result in significant savings during the intro period, but carries the risk of higher payments once the rate resets.
This ARM calculator models the full lifecycle of an adjustable-rate loan. Enter your loan details, the introductory rate and period, the expected adjusted rate, and the adjustment caps. The calculator shows your payment during the intro phase, the projected payment after the first adjustment, and the total interest cost over the full term.
ARMs are most advantageous for borrowers who plan to sell or refinance before the first rate adjustment. If you expect to stay in the home long-term, comparing the ARM's total cost against a fixed-rate alternative helps you make the right choice.
ARMs can save thousands during the introductory period, but the future payment uncertainty makes it critical to model worst-case scenarios before signing. This calculator lets you see exactly what happens at the first adjustment and compare the ARM's total cost against a fixed-rate mortgage.
Whether you are a first-time buyer considering a 5/1 ARM or a move-up buyer planning to sell within seven years, understanding the numbers prevents payment shock and helps you choose the loan structure that fits your timeline.
Intro Payment: M₁ = P × [r₁(1+r₁)^n₁] / [(1+r₁)^n₁ − 1] where r₁ = intro rate / 12 / 100, n₁ = intro years × 12 (payments applied against full-term amortization) Remaining Balance after intro: computed from amortization schedule Adjusted Payment: M₂ = B × [r₂(1+r₂)^n₂] / [(1+r₂)^n₂ − 1] where B = remaining balance, r₂ = adjusted rate / 12 / 100, n₂ = remaining months
Result: Intro: $2,209/mo → Adjusted: $2,595/mo
A $400,000 5/1 ARM at 5.25% has an intro payment of $2,209/month for 5 years. After 60 payments the balance is ~$367,400. If the rate adjusts to 7.0% for the remaining 25 years, the new payment jumps to $2,595/month — a $386 increase. Total interest over 30 years is roughly $456,000, compared to $445,000 on a 6.5% fixed (depending on actual adjustment path).
During the introductory period, your payment is calculated using the teaser rate and the full loan term — meaning you are not just paying interest, you are also amortizing principal. When the intro period ends, the lender recalculates your payment using the new rate (index + margin) and the remaining balance over the remaining term. This recalculation can produce a significant payment increase, commonly called payment shock.
ARM caps protect borrowers from extreme rate increases. A typical 2/2/5 cap structure means the rate can increase by a maximum of 2% at the first adjustment, 2% at each subsequent annual adjustment, and 5% total over the life of the loan. So if your intro rate is 5.25%, your lifetime maximum rate would be 10.25%.
ARMs outperform fixed-rate mortgages in two scenarios: when the borrower sells or refinances during the intro period, and when market rates decline after the intro period. Historical data shows that many ARM borrowers who planned to move within 5-7 years saved $10,000-$30,000 compared to a fixed-rate alternative.
A 5/1 ARM has a fixed interest rate for the first 5 years, then the rate adjusts once per year for the remaining term. The "5" is the fixed period and the "1" is the adjustment frequency. Common variants include 3/1, 7/1, and 10/1 ARMs.
ARMs have caps that limit rate changes. A typical cap structure is 2/2/5 — meaning the rate can increase up to 2% at the first adjustment, up to 2% at each subsequent adjustment, and up to 5% over the life of the loan.
ARMs carry interest-rate risk — if market rates rise, your payment increases after the intro period. However, if you plan to sell or refinance before the first adjustment, you benefit from the lower intro rate without experiencing the adjustment.
An ARM is most suitable if you plan to move or refinance within the introductory period. It also makes sense if you expect rates to decline, or if you need the lower initial payment to qualify for a larger loan amount.
Most modern ARMs use the Secured Overnight Financing Rate (SOFR) as the index. Older ARMs may reference LIBOR (being phased out), the 1-year Treasury, or the Cost of Funds Index (COFI). Your adjusted rate = index + lender margin.
Yes. Many ARM borrowers refinance into a fixed-rate mortgage before or shortly after the first adjustment. This is a common strategy to lock in certainty once you decide to stay in the home long-term. Factor in closing costs when evaluating this option.
It depends on how long you keep the loan and how rates move. If you sell during the intro period, the ARM almost always costs less. If you hold the loan for 30 years and rates rise, the fixed rate typically wins. This calculator helps you compare both scenarios.
Yes. When the intro period ends, your payment recalculates based on the new rate and remaining balance. The jump can be hundreds of dollars per month. This calculator shows you the exact projected increase so there are no surprises.