Estimate ARM payment changes
If expected future rate is blank, the calculator uses expected index plus margin. Enter principal and interest only; taxes, insurance, PMI, escrow changes, refinance costs, and tax effects are not modeled.
| Path | First payment | First adjusted rate | Adjusted payment | Peak payment | Total paid | Interest | Remaining balance |
|---|
Methodology notes
Payment resets
The initial payment is amortized over the full term. At each modeled adjustment, the payment is recalculated from the current balance, new capped rate, and remaining months.
Expected path
The expected rate uses the future rate field, or index plus margin if that field is blank. First and later increases are limited by the cap fields and lifetime cap.
Worst-case path
The capped path increases by the maximum allowed at each adjustment until the lifetime cap is reached, then compares the highest payment with the initial payment.
Results are estimates for educational purposes only and are not financial advice. Actual ARM notes may include floors, rounding rules, lookback dates, conversion options, negative-amortization protections, and servicer-specific payment timing. See full disclosure.
ARM mortgage FAQ
What is payment shock?
Payment shock is the increase from the initial principal-and-interest payment to the adjusted payment. This calculator shows both expected first-adjustment shock and worst-case capped shock.
What if I sell before the intro period ends?
The ARM may have a lower payment while you hold the loan, but the risk is that plans change. Compare the fixed-rate option and worst-case payment before relying on a short horizon.
Why do index and margin matter?
Most ARMs reset to an index plus a fixed margin, subject to caps and floors. Your lender's note terms control the exact formula and timing.