30-year fixed vs 7/1 ARM (US): 30-year lifetime interest
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By Editorial team
A $525,000 US home with 20% down leaves a $420,000 conventional loan. Compare a 30-year fixed at 6.85% with a 7/1 ARM at 6.10% and the first-year P&I difference is roughly $207/month. Over the modeled 30-year life, scheduled interest totals about $570,752 on the fixed path versus $486,919 on the ARM path. This is for US buyers comparing a 7/1 ARM against a 30-year fixed who want to see both the payment savings and the rate-reset risk modeled together.
The scenario modeled
The ARM holds its 6.10% rate for the first seven years. After that, it adjusts annually based on a benchmark rate (modeled at 4.20%) plus a 1.75% margin, subject to standard adjustment caps. The calculator shows what each reset looks like before it happens.
| Input | Fixed | 7/1 ARM |
|---|---|---|
| Loan amount | $420,000 | $420,000 |
| Product | 30-year fixed | 30-year ARM (7/1) |
| Start rate | 6.85% | 6.10% |
| MI | None (20% down) | None (20% down) |
The findings
Month-one P&I lands near $2,752 on the fixed loan versus $2,545 on the ARM. The $94,000 interest saving assumes the modeled adjustment path holds. If the index rises 1% above the modeled level after year 7, payments increase by roughly $50/month and the interest advantage narrows. Run a second tab with a higher index assumption before treating the $94,000 figure as a target.
For Canadian readers, "variable" usually points to a different set of renewal and payment rules. Read the Canada fixed vs variable guide when your closing is north of the border.
| Fixed | ARM | Difference | |
|---|---|---|---|
| Month 1 P&I | $2,752 | $2,545 | $207/month lower ARM |
| Total interest (modeled) | $570,752 | $486,919 | $83,833 less ARM |
| Rate risk after year 7 | None | Resets with caps | Model a rate stress scenario |
US context
The CFPB requires lenders to give ARM borrowers a plain-language disclosure showing how payments could change at each adjustment. Read that document alongside any calculator output, and compare it against the scenarios you run in the second tab.
Source: Consumer Financial Protection Bureau (CFPB), "What is an adjustable-rate mortgage?" accessed April 2026. URL: https://www.consumerfinance.gov/ask-cfpb/what-is-an-adjustable-rate-mortgage-en-100/
When this comparison applies, and when it does not
Helpful when you have a firm plan to sell or refinance within seven years, can tolerate payment variance after the fixed window closes, or want to pay the loan aggressively before adjustments take effect.
Poor fit when your budget cannot absorb a meaningful payment jump in year 8, you relocate frequently, or you have not modeled the worst-case cap scenario. Fixed rate may be worth the premium for the certainty alone.
Related articles
Frequently asked questions
- Is an adjustable-rate mortgage the same as a variable-rate mortgage?
- In US marketing, "variable" usually maps to adjustable-rate mortgages (ARMs) with disclosed index, margin, and caps. Canada’s contract terms differ. This page focuses on US fixed versus ARM trade-offs and links to Canadian guides for VRM wording.
- Why can an ARM show less lifetime interest than a fixed loan in a calculator?
- If the modeled ARM starts at a lower note rate and future adjustments stay inside the cap path you program, scheduled interest can be lower than a higher fixed rate. That is a modeling assumption, not a promise of future market rates.
- How long should I expect to keep an ARM before the first rate change?
- The first number in product names like 7/1 describes years of fixed payments before the first adjustment in common US conventions. After that, the loan resets on the schedule spelled out in your note.
- Where can I read more about Canada’s fixed versus variable choice?
- Open the Canadian mortgage guides hub and read the fixed vs variable article there. It covers renewal and discount mechanics separately from US ARM caps.