10/1 ARM Calculator with Extra Payment & Interest Only Option

Have you ever considered how even a small change in your mortgage terms could lead to significant savings? The 10/1 ARM Calculator with Extra Payment & Interest Only Option is a powerful tool that allows borrowers to make informed financial decisions about their potential home loans. Understanding this calculator’s features and benefits is essential for those looking to optimize their mortgage payments and tailor their financing strategy effectively. In this article, we will explore how this calculator can enhance your budgeting and provide insights into managing your mortgage more efficiently.

10/1 ARM Calculator

Calculate your adjustable-rate mortgage payments with precision

Basic Loan Information

Loan Amount ($)

Initial Interest Rate (%)

Loan Term (Years)

ARM Adjustment Details

Note: The boxes below are for illustration purposes. You may adjust the values to match your specific loan terms.

Adjustment Frequency after initial fixed period

Note: The calculation boxes below are for illustration purposes. You can edit any field to explore different scenarios, and the totals will automatically update.

Margin + Index = Interest Rate

Margin (%)

Index (%)

Interest Rate (%)

Current Interest Rate + Annual Cap = Interest Rate

Current Interest Rate (%)

Annual Cap (%)

Interest Rate (%)

Lifetime Interest Rate Cap (%)

Annual Rate Cap (%)

Optional Settings

Interest-only payments during initial fixed period

Disclaimer: Interest-only options are not standard for FHA loans. This scenario is for illustrative comparison purposes only.

Extra Principal Payment ($/month)

Payment Summary

Initial Monthly Payment

Your fixed payment for the first 10 years

First Adjustment Payment

Year 11 payment (rate + 1%)

Maximum Payment

At lifetime cap (initial rate + 5%)

Total Interest (Worst-Case)

Based on +1% annual increases to cap

Amortization Schedule (Worst-Case Scenario)

Shows rates increasing by 1% annually after year 10, up to the lifetime cap

Year	Rate	Monthly Payment	Principal	Interest	Balance

How to Find the Current Index Rate

Calculating the adjustment rate can be tricky, but it doesn't have to be. The confusion often stems from the index rate. The boxes above offer a clear visual of how your new interest rate is set.
Here are the best sources for the 1-Year CMT index used for FHA ARMs:

1. U.S. Department of Treasury (Official Source)
> Daily Treasury Par Yield Curve Rates: https://home.treasury.gov/resource-center/data-chart-center/interest-rates/TextView?type=daily_treasury_yield_curve
Click "Apply" and look under the one-year column. Scroll to the bottom of the table to see the current index rate.

2. Easiest Option – Federal Reserve Bank of St. Louis (FRED)
> 1-Year Treasury Constant Maturity Rate: https://fred.stlouisfed.org/series/DGS1
In the top-left corner, under "Observations," you'll see the current index rate.

As of this writing, the index rate was 3.59%. Enter 3.59 in the index box above. Your lender will provide the margin, which is the additional percentage they charge. This margin remains fixed for the life of the loan. Add the index rate and margin together to find your current interest rate.

Understanding Your FHA ARM Index Rate

But what happens if the index rate spikes? That's where rate caps protect you. For this ARM, the interest rate can increase by no more than 1% per year (every 12 months) until it reaches the lifetime cap of 5%. After entering your numbers, review the worst-case amortization schedule to see how payments could adjust over time.

Ask the lender when the new interest rate is calculated. For example: The lender calculates the new rate at the end of the initial term (e.g., after 10 years for a 10/1 ARM), and the new rate will apply for the next adjustment period.

This calculator is designed to help you clearly understand how an FHA adjustable-rate mortgage works - and to give you the confidence to manage it wisely.