ARM Calculator

Calculate your adjustable-rate mortgage payments with precision

An adjustable rate calculator is essential for understanding how your mortgage payment can change. This tool provides a detailed loan payment breakdown, helping you compare fixed vs adjustable rates, plan for interest rate fluctuations, and manage borrowing costs.

Basic Loan Information

ARM Type

Treasury Rate Source

Loan Amount ($)

Initial Interest Rate (%)

Loan Term (Years)

ARM Adjustment Details

Federal Reserve Bank of St. Louis (FRED) - 1-Year Treasury Rate: (Index %)
Visit: https://fred.stlouisfed.org/series/DGS1
In the top-left corner, under "Observations," you'll see the current index rate.

Once you find the current index rate, enter it in the Index (%) field below.

Note: This calculator works for FHA, VA, and conventional ARMs. After the initial fixed period ends, the rate will adjust annually based on your loan's index and margin. The calculation boxes below are for illustration purposes — you can edit any field to explore different scenarios.

Margin + Index = Interest Rate

Margin (%) Get from lender

Index (%) from above

Interest Rate (%)

Current Interest Rate + Annual Cap = Interest Rate

Current Interest Rate (%)

Annual Cap (%)

Interest Rate (%)

Lifetime Cap (% above initial rate)

Example: If initial rate is 6.5% and lifetime cap is 5%, the maximum rate is 11.5%

Optional Settings

Interest-only payments period

Interest-Only Period Duration (Years)

Enter number of years for interest-only period

Note: During the interest-only period, you'll pay only the interest on the loan each month. Principal payments will begin after this period ends.

Extra Principal Payment ($/month)

Expected Rate Adjustment (%/year)

Payment Summary

Initial Monthly Payment

Your fixed payment for the first 5 years

First Adjustment Payment

Year 6 payment (rate + adjustment)

Maximum Payment (Theoretical)

At lifetime cap

Total Interest Paid

Based on modeled rate adjustments

Total Cost (Principal + Interest)

Loan amount + total interest

Early Payoff

Loan pays off early due to extra payments

Complete Amortization Schedule

Year	Rate	Monthly Payment	Principal Paid	Interest Paid	Remaining Balance