ARM vs. Fixed Rate Mortgage Calculator

ARM vs. Fixed Rate Calculator

ℹ RefinanceUSA is not a lender. Results are estimates — "projected" assumes the ARM adjusts to your projected rate; "worst case" assumes the ARM hits the per-adjustment cap every year. How we calculate

How Adjustable Rate Mortgages Work

An ARM has two phases: a fixed-rate period (the initial teaser rate) and an adjustment period (when the rate resets annually based on an index). The most common ARMs are the 5/1 ARM (5 years fixed, adjusts every 1 year after) and 7/1 ARM.

Rate Caps: Your Protection Against Runaway Rates

ARM caps limit how much the rate can change. A common cap structure is 2/2/5:

• First cap (2%): The first adjustment after the fixed period cannot exceed the initial rate plus 2%.
• Periodic cap (2%): Each subsequent annual adjustment is also capped at 2%.
• Lifetime cap (5%): The rate can never exceed the initial rate plus 5%, no matter what happens to indices.

A 5/1 ARM at 6.0% with 2/2/5 caps: first adjustment can go to at most 8.0%. Second adjustment: up to 10.0%. Lifetime max: 11.0%. But the actual rate depends on the index (typically SOFR) plus the lender's margin.

ARM vs. Fixed: Payment Comparison

3 ARM vs. Fixed Scenarios

Scenario 1 — Selling in 5 years: ARM clearly wins

When the sale timeline is shorter than the ARM's fixed period, the ARM is a straightforward win. The lower initial payment saves $207/month with zero rate-adjustment risk. This is exactly the use case ARMs were designed for.

Scenario 2 — Staying 10 years: Fixed wins in the worst case

In the projected scenario (rate adjusts to 7%), the ARM costs slightly less over 10 years. In the worst case (caps out at 8%), the fixed loan saves $15,960 over 10 years. Whether the ARM's initial savings outweigh the adjustment risk depends entirely on what happens to rates after year 5.

Scenario 3 — ARM to fixed refinance: Locking in before adjustment

When an ARM is approaching its first adjustment and rates are elevated, refinancing to a fixed rate before the adjustment is often prudent. Even at a slightly higher fixed rate than the current ARM teaser, you're buying certainty against a potentially large adjustment. The refinancing cost break-even here is 15–23 months — well worth it if you plan to stay.

Frequently Asked Questions

What is a 5/1 ARM?

A 5/1 ARM has a fixed rate for the first 5 years, then adjusts annually. The adjustment is based on a reference index (usually SOFR) plus a lender margin. Rate caps protect against extreme movements — typically 2% per adjustment and 5% over the life of the loan.

When does an ARM make sense?

An ARM makes sense when (1) you plan to sell or refinance before the fixed period ends, (2) the initial rate discount vs. a fixed loan is 0.5%+, or (3) you expect interest rates to fall during the adjustment period. For long-term holds with no rate certainty, a fixed loan is generally lower risk.

What are ARM rate caps?

Caps limit annual and lifetime rate increases. A common 2/2/5 structure means: first adjustment is capped at initial rate + 2%, each subsequent adjustment at +2%, and total lifetime change is capped at +5%. A 6.0% ARM with 2/2/5 caps can never exceed 11.0%.

Should I refinance from ARM to fixed?

Yes, when (1) your ARM is approaching its first adjustment and current fixed rates are reasonable, (2) you plan to stay long-term, or (3) the projected adjustment would significantly increase your payment. Use the calculator above to model your specific adjustment scenario against available fixed rates.

What index do ARM loans use in 2026?

The Secured Overnight Financing Rate (SOFR), which replaced LIBOR in 2023. SOFR is based on overnight US Treasury repo transactions and is published daily by the New York Federal Reserve. Your lender adds a fixed margin (typically 2.5%–3.5%) to SOFR to calculate your adjusted rate. The fully indexed rate — SOFR plus margin — is what your ARM would cost if it adjusted today, before cap limits. Ask your lender for this number when evaluating an ARM.

Can I convert my ARM to a fixed rate without refinancing?

Some ARMs include a built-in conversion option that allows you to lock into a fixed rate during a specified window, usually between years 1 and 5 of the loan. The converted fixed rate is typically the prevailing market rate at conversion plus a spread, and a conversion fee applies. This option is rare on most conventional ARMs today. In most cases, converting to fixed requires a full refinance with closing costs and a new rate based on current market conditions.

Do ARMs have prepayment penalties?

Most US ARM loans on owner-occupied homes do not have prepayment penalties, particularly Qualified Mortgages (QMs) that comply with CFPB ability-to-repay rules. Non-QM portfolio ARMs — offered by some private lenders — may include prepayment penalty clauses. Check your loan documents under the "Prepayment Penalty" section before signing. The Loan Estimate also discloses whether a prepayment penalty applies on Page 1 in the "Loan Terms" box.

How to Use the ARM vs. Fixed Calculator

This calculator models your specific ARM — initial rate, fixed period, cap structure, and projected adjustment — against a fixed-rate alternative over your expected hold period. Here is how to fill in each field for accurate results.

Step 1 — Enter your loan amount and expected stay

The "expected stay" field is the most important input. If you plan to sell in 6 years, enter 6 — the calculator then shows ARM vs. fixed total cost over exactly that window. The lifetime comparison is secondary; what matters is the period you'll actually own the home.

Step 2 — Fill in the ARM details from your Loan Estimate

Enter the initial rate, fixed period (e.g., 5 years for a 5/1 ARM), and cap structure. Your Loan Estimate's ARM disclosure page lists the initial cap (first adjustment limit), periodic cap (each subsequent adjustment), and lifetime cap. A 2/2/5 cap structure is standard — enter those values directly.

Step 3 — Set the projected rate after the fixed period

The calculator models two ARM paths: your projected rate (best estimate of where rates will be) and a worst-case path (rate hits the per-adjustment cap every year until the lifetime cap). Check the SOFR index plus your lender's margin to estimate the projected adjusted rate. The margin is disclosed on your ARM Loan Estimate and typically runs 2.5%–3.5%.

Step 4 — Compare projected vs. worst-case outcomes

If the ARM saves money even in the worst-case scenario, it is a low-risk choice. If the ARM only wins in the projected scenario, you are making a bet on future rates. The verdict line shows which situation applies to your inputs.

The Hold Period Rule of Thumb

A simple guide: if your expected stay is shorter than the ARM's fixed period, the ARM almost always wins — you exit before any rate adjustment risk materializes. If your stay is longer than the fixed period, the ARM's advantage depends entirely on what happens to rates after the first adjustment. Use the ARM vs. Fixed guide to understand cap structures and realistic adjustment scenarios before deciding.

ARM Types: 3/1, 5/1, 7/1, 10/1 — Match Your Timeline

The notation "X/Y ARM" means: fixed for X years, then adjusts every Y year(s). The Y is almost always 1 (annual adjustments) in today's US mortgage market. Choosing the right ARM type depends entirely on how long you plan to stay in the home.

Rate Spread: ARM vs. 30-Year Fixed

The ARM advantage — its lower initial rate vs. a 30-year fixed — is called the spread. In a normal (upward-sloping) yield curve, typical spreads are:

• 3/1 ARM: ~0.75%–1.25% below 30-yr fixed
• 5/1 ARM: ~0.50%–1.00% below 30-yr fixed
• 7/1 ARM: ~0.25%–0.75% below 30-yr fixed
• 10/1 ARM: ~0.125%–0.50% below 30-yr fixed

When the spread compresses below 0.25%, the ARM's savings rarely justify its adjustment risk. Always check the current ARM-to-fixed spread before assuming an ARM is the cheaper choice — in inverted yield curve environments, the spread can disappear entirely or even invert.

The One-Cycle Buffer Rule

If your expected hold is exactly 5 years, don't choose a 5/1 ARM — choose a 7/1. A delayed sale, a change of plans, or a slow market can push your exit past the fixed period end date. The one-cycle buffer rule: select an ARM whose fixed period is at least 2 years longer than your most likely exit date. The incremental cost of the longer ARM type is usually small; the downside of missing the exit window is a potentially large rate adjustment.

How Your ARM Rate Is Calculated After the Fixed Period

After the fixed period ends, your ARM rate resets annually. The formula is simple: Your Rate = Index + Margin, subject to cap limits. Understanding both components helps you project your future payment accurately.

The Index: SOFR (Replaced LIBOR in 2023)

Since June 2023, all new US ARM loans use SOFR — the Secured Overnight Financing Rate — as the index. SOFR is based on daily overnight Treasury repo transactions published by the New York Federal Reserve. It replaced LIBOR, which was discontinued after manipulation scandals.

• SOFR is more transparent than LIBOR — based on actual transactions, not bank estimates
• SOFR rates are published daily at newyorkfed.org
• Your loan documents specify a lookback period (typically 45–90 days before each adjustment date) — that date's SOFR is the value used
• Existing LIBOR ARMs were converted to SOFR in 2023 using specified spread adjustments mandated by the LIBOR Act

The Margin: Fixed for the Life of the Loan

Your lender's margin is fixed at origination and never changes. It is disclosed on the ARM disclosure page of your Loan Estimate. Typical margins run 2.5%–3.5% depending on the lender and loan type. Example: if SOFR is 4.5% and your margin is 2.75%, your fully indexed rate is 7.25% — before cap limits apply.

Projecting Your Adjusted Rate

Use current SOFR from the New York Fed website plus your margin from your loan documents to project your rate. Then apply cap limits: first adjustment cannot exceed initial rate + first-adjustment cap; each subsequent adjustment cannot exceed previous rate + periodic cap; total lifetime change cannot exceed the lifetime cap. The lowest number among (fully indexed rate), (previous rate + periodic cap), and (initial rate + lifetime cap) governs each adjustment.

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