Fixed vs Variable Interest Rate: Which is Better?

How fixed vs variable interest rate works in practice

A fixed interest rate stays constant for the agreed term. A variable (adjustable) rate changes periodically based on an index like SOFR, prime rate, or a central bank benchmark, plus a lender margin.

The goal is not to memorize every term — it is to know which inputs matter and what outcome you are aiming for.

So what: When you can explain this in your own words, you are far less likely to accept a bad quote, fee, or assumption.

A real scenario worth running

$400,000 mortgage — 6.5% fixed vs 5.5% variable that rises to 7.5% after 5 years. Step by step: Fixed at 6.5%: payment ≈ $2,528/month for 30 years → Variable starts at 5.5%: payment ≈ $2,271/month initially → If variable rises to 7.5%: payment jumps to ≈ $2,797/month. Bottom line: Variable saves ~$257/month initially but could cost $269/month more than fixed if rates rise — $3,228/year extra.

So what: Plug your own numbers into the same logic before you decide.

Fixed vs variable: the core trade-off

Fixed rate: Interest rate locked for entire loan term — payment never changes (on fully amortizing fixed loans).

Variable rate (ARM): Rate tied to a benchmark (SOFR, prime) — adjusts on a schedule after an initial fixed period.

You're trading certainty (fixed) for initial savings (variable). The right choice depends on how long you'll hold the loan and your tolerance for payment shocks.

So what: Run your own inputs before you commit — small changes in assumptions can shift the outcome sharply.

Fixed rate — pros and cons

Pros:

• Payment never changes — easy to budget decades ahead
• Protected if market rates rise sharply
• No surprise payment increases
• Simpler mental model for first-time buyers

Cons:

• Usually starts 0.5–1%+ higher than variable teaser rates
• No automatic benefit if market rates fall (must refinance)
• Refinancing costs 2–5% of loan and takes time

So what: Run your own inputs before you commit — small changes in assumptions can shift the outcome sharply.

Variable rate — pros and cons

Pros:

• Lower initial rate — saves money in early years
• Payments can decrease if benchmark rates fall
• Good for short ownership (sell before adjustment)
• Rate caps limit worst-case increases

Cons:

• Payment uncertainty — hard to budget long-term
• Rate spikes can strain finances (2008, 2022 examples)
• Requires understanding caps, margins, and adjustment periods
• Payment shock when fixed period ends

So what: Run your own inputs before you commit — small changes in assumptions can shift the outcome sharply.

Worked example: $300,000 loan, 30-year

ARM wins if you sell or refinance within 5 years. Fixed wins if rates rise and you stay 10+ years.

So what: Run your own inputs before you commit — small changes in assumptions can shift the outcome sharply.

Decision framework

So what: Run your own inputs before you commit — small changes in assumptions can shift the outcome sharply.

Key ARM terms to check

5/1 ARM at 5.5% with 2% periodic cap and 5% lifetime cap:

• Max rate year 6: 7.5% (if index spikes)
• Absolute max over life: 10.5%

Always model worst-case payment at lifetime cap — not just teaser rate.

So what: Run your own inputs before you commit — small changes in assumptions can shift the outcome sharply.

Fixed vs variable by loan type

So what: Run your own inputs before you commit — small changes in assumptions can shift the outcome sharply.

When refinancing makes sense

Refinance fixed → lower fixed when rates drop 0.5–1%+ and you'll stay 3+ years.

Refinance ARM → fixed when:

• Intro period ending and rates rising
• Payment shock would exceed budget
• You plan to stay long-term

Closing costs typically $3,000–$8,000 — divide by monthly savings to find break-even months.

So what: Run your own inputs before you commit — small changes in assumptions can shift the outcome sharply.

Common mistakes

1. Fixed = predictable payments; variable = potential savings or risk — this quietly costs you over time.
2. Variable rates often start lower than fixed — the 'teaser' advantage..
3. Rate caps limit how much a variable loan can increase per period — this quietly costs you over time.
4. Fixed suits long-term homeowners; variable suits short-term holders — this quietly costs you over time.
5. Always model worst-case variable scenarios before borrowing — this quietly costs you over time.

What to do next

Use our Compare Mortgage Payments to model your situation — change one input at a time to see what moves the result most.