The Calculator App
ARM Calculator
Estimate an adjustable-rate mortgage from a starting rate, a product, caps, and a scenario rate you enter. Payments after the fixed period follow that scenario. This is not a rate forecast.
$2,018.41 / month
Illustrative 5/1 using a $400,000 price, 20% down, a 6.48% starting rate, and a 6.75% scenario rate. Highest modeled principal and interest $2,069.18. Not a quote. The interactive calculator replaces this summary in the browser.
How an ARM payment changes
The starting rate stays in place for the fixed period of the product you select. At each adjustment date the rate moves toward the scenario rate, limited by the caps, and the remaining balance is reamortized. That path is a scenario you control. It is not a rate forecast.
Questions
What is an adjustable-rate mortgage?
An adjustable-rate mortgage keeps the rate you enter for a fixed period, then can change on a schedule. A 5/1 changes after five years and then once a year. A 5/6 changes after five years and then every six months. This page uses that timing. It does not look up an index.
How do ARM caps work?
The initial cap limits the first change. The periodic cap limits each later change. The lifetime cap limits how far the rate can rise above the starting rate. The lifetime floor is the lowest rate this scenario will use. The payment is recalculated on the remaining balance and the remaining term after each change.
Is the future rate a forecast?
No. The scenario rate is a figure you type. After the fixed period, the model moves toward that figure and stops at the caps. The margin and index are recorded with the scenario. They are not added together to produce the rate, and they are not a prediction of a future index.
How does this compare with a fixed-rate loan?
The fixed comparison uses the same price, down payment, term, and starting rate with adjustments turned off. The initial principal and interest match. Later ARM payments can be higher or lower only because of the scenario rate and the caps. A lower starting payment is not treated as a lower total cost.
What is included in the monthly amount?
The initial payment is principal and interest at the starting rate. Taxes, insurance, mortgage insurance, HOA, and other costs are added only when you include them. Those costs stay flat in this scenario. The chart of the payment path shows principal and interest, which is the part that changes when the rate adjusts.