ARM Mortgage Calculator

Calculate adjustable-rate mortgage payments with rate caps. See worst-case scenario vs fixed rate.

By Konstantin Iakovlev · Updated September 2026 · Source: CFPB — Rate caps on an adjustable-rate mortgage

$
%
Initial Period
%
%
%
%
%

Initial Payment

$2,271.16

Worst-Case Payment

$3,491.98

30yr Fixed Payment

$2,594.39

ARM vs Fixed Comparison

Initial ARM Payment$2,271.16
30yr Fixed Payment$2,594.39
Monthly Savings (first 5 yrs)$323.24
Total Savings (first 5 yrs)$19,394.18
First Adjustment Rate7.25%
First Adjustment Payment$2,673.25
Worst Case Rate (lifetime cap)10.50%
Worst Case Payment$3,491.98

Rate Adjustment Schedule

Initial (Years 1-5)$2,271.16
Year 6 — 7.25%$2,673.25
Year 7 — 7.25%$2,673.25
Year 8 — 7.25%$2,673.25
Year 9 — 7.25%$2,673.25
Year 10 — 7.25%$2,673.25

Use the ARM Mortgage Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.

Disclaimer: This calculator is for informational purposes only and does not constitute tax, financial, or legal advice. Results are estimates based on the information you provide and current rates. Always consult a qualified tax professional or financial advisor for advice specific to your situation.

How It Works

Payments on an Adjustable-Rate Mortgage (ARM) move as interest rates do, and this tool traces how yours could shift across the life of the loan. Seeing those swings ahead of time is what makes it possible to budget honestly and weigh the long-term affordability and risk of choosing an ARM in the first place.

The math begins with the introductory fixed-rate payment, derived from standard amortization formulas. Once that fixed period ends, the calculator re-runs the numbers at each scheduled adjustment, applying a fresh interest rate built from an index plus a margin and constrained by the loan's periodic and lifetime caps.

Borrowers most often get tripped up by assuming rates will stay tame, then overlooking how high the lifetime cap actually allows payments to climb. Run the figures against a meaningful rate increase so you know the loan still fits your budget even when the market turns against you.

Example: A 5/1 ARM at Its First Adjustment

  1. 1 Imagine a $400,000 mortgage at an initial 5.5% for 5 years, with a 2% adjustment cap, a 5% lifetime cap, a 2.75% margin and an index of 4.5%, compared with a 6.75% 30-year fixed rate.
  2. 2 Initial payment: $2,271.16 a month on a 30-year schedule, $323.24 less than the $2,594.39 fixed-rate payment, or $19,394.18 over the first 5 years. After 60 payments the balance is $369,842.41.
  3. 3 First adjustment: index + margin = 4.5% + 2.75% = 7.25%, inside the 2% cap (5.5% + 2% = 7.5%). Re-amortized over the remaining 25 years, the payment rises to $2,673.25, $402.09 more than before.
  4. 4 Worst case: the 5% lifetime cap allows up to 10.5%, and at that rate the payment on the same balance would be $3,491.98. That is the number to test your budget against before choosing an ARM.

Source: CFPB — Rate caps on an adjustable-rate mortgage · Last updated: September 2026

Frequently Asked Questions

How does an adjustable rate mortgage work?
An ARM has a fixed rate for an initial period (typically 5, 7, or 10 years), then adjusts annually based on a benchmark index plus a margin. A 5/1 ARM is fixed for 5 years, then adjusts every 1 year.
What are ARM rate caps?
ARMs have three caps: initial adjustment cap (how much the rate can change at the first adjustment, commonly 2% or 5%), periodic cap (maximum change at each later adjustment, most commonly 1% or 2%), and lifetime cap (maximum total change, most commonly 5%). The calculator uses a single adjustment cap for every adjustment. A 5/1 ARM starting at 5.5% with a 5% lifetime cap cannot exceed 10.5%.
When does an ARM make sense over a fixed rate?
An ARM makes sense if you plan to sell or refinance before the fixed period ends, or if ARM rates are significantly lower than fixed rates. If you will stay in the home long-term through rate adjustments, a fixed rate provides more predictable payments.

You might also need

Mortgage Calculator 2026 — Payment, Amortization & PMI

Calculate your monthly mortgage payment with taxes, insurance, PMI, and HOA. Free, instant results at the interest rate you enter.

FHA Loan Calculator 2026 — MIP, Down Payment & Limits

Calculate FHA loan payments including upfront MIP (1.75%) and annual MIP premiums. See when MIP drops off. Free, instant results based on 2026 FHA limits.

Home Affordability Calculator — How Much House Can You Afford?

Find out how much house you can afford based on income, debts, down payment, and the mortgage rate you enter. Free, instant results with DTI ratio breakdown.