ARM Mortgage Calculator
Last updated: October 15, 2026
Compare an adjustable-rate mortgage payment before and after the first rate reset.
Payment after first reset
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- Initial monthly payment: —
- Balance at reset: —
- Monthly payment change: —
On this page
Quick summary: Compare an adjustable-rate mortgage payment before and after the first rate reset.
Read the complete guide
Updated reference sections in this guide are in English.
What this calculator estimates
Compare an adjustable-rate mortgage payment before and after the first rate reset.
How to use it
Enter Loan amount ($); Initial interest rate (%); Initial fixed period (years); Rate after reset (%); Total loan term. Select Calculate to update the results.
How the calculation works
Let P be the loan amount, r the annual percentage rate divided by 1200, and n the total months. A monthly payment is P × r / (1 - (1+r)^(-n)); at zero interest it is P/n. First calculate the initial payment, then the outstanding balance after the initial fixed period. Re-amortize that balance at the entered reset rate over the remaining months. The displayed change is the new payment minus the initial payment.
Worked example: starting scenario
| Loan amount ($) | 400000 |
|---|---|
| Initial interest rate (%) | 5.5 |
| Initial fixed period (years) | 5 |
| Rate after reset (%) | 7 |
| Total loan term | 30 years |
| Payment after first reset | $2,613.97 |
|---|---|
| Initial monthly payment | $2,271.16 |
| Balance at reset | $369,842.41 |
| Monthly payment change | $342.81 |
Important limitations
This scenario models one reset, followed by an unchanged rate. It does not select an index or margin, apply periodic or lifetime rate caps, or include taxes, insurance, fees or later resets. The initial fixed period must be shorter than the total term. A lender's contractual schedule can differ.