ARM Mortgage Calculator

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

By Konstantin Iakovlev · Updated April 2026 · Source: CFPB — Owning a Home

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Initial Period
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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%$2,713.18
Year 8 — 7.25%$2,757.47
Year 9 — 7.25%$2,806.71
Year 10 — 7.25%$2,861.64

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: ARM Payment Adjustment

  1. 1 Imagine a $300,000 mortgage with an initial 5% interest rate for 5 years (5/1 ARM). After 5 years, the index is 3% and the margin is 2%, resulting in a new rate of 5%.
  2. 2 Initial payment for a 30-year term at 5% would be approximately $1,610.46. After 5 years, with the new rate still at 5% (due to index + margin), and a remaining principal of about $276,432 over 25 years, the payment would remain very similar.
  3. 3 Initial monthly payment: ~$1,610.46. After 5 years, if the rate adjusts to 5%, the new monthly payment would be approximately $1,618.00.
  4. 4 In this scenario, the rate didn't change significantly, leading to a minor payment increase. This highlights the importance of understanding how index and margin combine to determine your new rate, and how even small changes can impact your budget.

Source: CFPB — Owning a Home · Last updated: April 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. Initial ARM rates are typically 0.5-1.5% lower than fixed rates.
What are ARM rate caps?
ARMs have three caps: initial adjustment cap (how much the rate can change at first adjustment, typically 2%), periodic cap (maximum change per adjustment period, typically 2%), and lifetime cap (maximum total increase, typically 5%). 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.

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