Why Compare These Two Mortgage Types?
Your mortgage rate shapes your monthly budget and your long-term financial future. Here’s why this comparison matters:
- 📉 Lower Initial Payments — ARMs typically start with rates 0.50% to 1.50% lower than fixed-rate loans, giving you more breathing room early on
- 🛡️ Rate Protection Built In — Lifetime caps on ARMs prevent runaway rate increases, so you know your worst-case scenario
- ⏳ Strategic Flexibility — Ideal if you’re planning to move, upgrade, or refinance within 5–7 years
- 📊 See the Full Picture — Side-by-side projections show monthly payments, total interest, and year-by-year trajectories over the full 30-year term
- 🌍 170+ Currencies Supported — All amounts format automatically to your local currency
- 🔒 100% Private — Everything runs locally in your browser; your financial data never leaves your device
The Math Behind It (Made Simple)
Fixed-Rate Monthly Payment
Fixed Payment = Loan Amount × Monthly Rate × (1 + Monthly Rate)^Total Payments ÷ ((1 + Monthly Rate)^Total Payments − 1)
- Monthly Rate = Annual Rate ÷ 12
- Total Payments = Years × 12
ARM Rate After Adjustment
ARM Rate After t Years = The lower of: 1. Initial Rate + (t × Annual Increase) 2. Lifetime Maximum Cap
Side-by-Side Example: $400,000 Home Loan
Here’s how a 5/1 ARM stacks up against a 30-Year Fixed mortgage:
| Metric | 30-Year Fixed (6.75%) | 5/1 ARM Initial (5.50%) | 5/1 ARM Max Cap (10.50%) |
|---|---|---|---|
| Monthly Payment | $2,594 | $2,271 | $3,658 |
| Monthly Savings (Years 1–5) | — | +$323/month | −$1,064/month |
| 5-Year Cumulative Savings | — | +$19,388 | N/A |
| 30-Year Total Interest | $533,948 | Varies | Max $780,000+ |
Which One Should You Choose?
Go With a Fixed-Rate Mortgage If:
- You’re staying put — planning to live in the home for 10, 15, or 30 years
- You crave stability — you want predictable payments that never change
- Rates are low — you’re locking in a historically favorable rate
Go With an ARM If:
- You’re not staying long — planning to sell or move within 3–7 years
- You’ll refinance — you expect rates to drop before your intro period ends
- You’ll pay extra — you plan to make large principal payments during the low-rate period
How to Use This Calculator
- Pick your currency from the global selector in the site header.
- Enter your loan amount (e.g., $400,000).
- Input the fixed mortgage rate offered by lenders (e.g., 6.75%).
- Input the ARM initial rate (e.g., 5.50%).
- Set the ARM intro period — 5, 7, or 10 years.
- Add expected annual rate increases and the maximum rate cap.
- View instant results — compare monthly payments, total interest, and switch between charts.
Common Questions About ARM vs Fixed Mortgages
What’s the difference between a Fixed-Rate and ARM?
A fixed-rate mortgage keeps the same interest rate and payment for the entire loan term — usually 15 or 30 years. An ARM starts with a lower introductory rate for a set period (5, 7, or 10 years), then adjusts periodically based on market rates.
What do 5/1, 7/1, and 10/1 ARMs mean?
- The first number = how many years the initial fixed rate lasts (5, 7, or 10 years).
- The second number = how often the rate adjusts afterward (1 = once per year).
When does an ARM make sense?
If you plan to sell, move, or refinance before the introductory period ends, an ARM can save you thousands in interest. It’s also a good fit if you expect your income to grow or plan to pay down principal aggressively.
What are ARM rate caps?
Caps protect you from runaway rate increases: - Initial cap — limits the first rate change - Periodic cap — limits annual adjustments after that - Lifetime cap — sets the absolute maximum rate over the life of the loan