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 meaningful savings during the intro period, but it also carries the risk of higher payments once the rate resets.
This ARM calculator models a simplified two-stage ARM path. Enter your loan details, the introductory rate and period, and a single expected adjusted rate after the intro period ends. 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. It does not simulate every later adjustment, index path, or cap step.
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 projected cost against a fixed-rate alternative helps you make the tradeoff explicit.
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: $2,605/mo
A $400,000 5/1 ARM at 5.25% has an intro payment of about $2,209/month for 5 years. After 60 payments the balance is about $368,598. If the rate resets to 7.0% for the remaining 25 years, the payment becomes about $2,605/month — roughly $396 more per month. In this simplified two-stage path, total ARM interest is about $514,081 versus about $558,036 on a 30-year fixed loan at 7.0%.
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 can come out ahead when the borrower sells or refinances during the intro period or when future rates fall rather than rise. But the comparison is path-dependent: fees, timing, refinance costs, and the actual reset path all matter. That is why this page is best used for scenario testing rather than for assuming the teaser rate automatically wins.
Last updated:
This worksheet models the ARM in two stages only: an introductory fixed-rate period amortized over the full loan term, followed by a single reset to the user-entered adjusted rate for the remaining balance and remaining months. It then compares that simplified path with a same-term fixed-rate loan at the entered adjusted rate.
It is a scenario-planning tool, not a complete ARM disclosure model. Real ARM contracts may adjust multiple times, apply index-plus-margin pricing, and limit changes through initial, periodic, and lifetime caps that are not fully simulated here.
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.