When I was building our Credit Union Mortgage Dashboard, I kept seeing this weird product pop up: the 15/15 ARM.
I asked an independent mortgage broker about it. He waved it off. “Niche product. Just go 30Y fixed at that point.”
But you know what’s not niche? 20 basis points.
For the average American home, that’s $50 a month. For a VHCOL area like the SF Bay Area, it’s $150 a month. Over the life of a loan, we’re talking tens of thousands of dollars.
The 15/15 ARM deserves a closer look.
What is a 15/15 ARM?
We all know the “ARM” (Adjustable Rate Mortgage) horror stories from 2008. But not all ARMs are created equal.
A 7/1 ARM adjusts once a year after 7 years. 5/1 adjusts annually after five years. 3/6 is fixed for three years and then adjusts every 6 months. You get it. And it seems like with each passing year, there’s a new type of mortgage with an even smaller fixed number. How about something bigger for a change?
A 15/15 ARM starts as fixed for 15 years. And that second 15 isn’t fifteen months. At year 16, it adjusts one time. Then it stays fixed for another 15 years.
As of 2025, the average American homeowner stays in a home for about 12 years. 15 years is an eternity.
If you sell your house in year 10? You paid a lower rate the entire time. If you refinance in year 7? You paid a lower rate the entire time. If you pay off the mortgage early? You paid a lower rate the entire time.
In all these cases, the 15/15 ARM leaves you with way more money in your pocket, with all the same security as a 30-year fixed, and a much lower monthly payment than a 15-year fixed mortgage.
The Math: Saving 20bps
Let’s look at the numbers from our Credit Union Dashboard.
- 30-Year Fixed Average: 5.92%
- 15/15 ARM Average: 5.72%
On a $500,000 loan:
- 30Y Fixed Payment: $2,972/mo
- 15/15 ARM Payment: $2,912/mo
Savings: $60/month, or $10,800 over the 15-year fixed period.
That is ten thousand dollars of risk-free savings, assuming you, like most people, move or refinance before year 15.
Who Offers This?
The 15/15 ARM is almost exclusively a Credit Union product—and even then, it’s not universal. In our sample of credit unions, only about 10% offer a 15/15 ARM.
Why so rare? Big banks don’t like it. It doesn’t fit neatly into the Wall Street securitization machine. Fannie Mae will buy them, but they’re not a priority.
The credit unions that do offer them tend to like how they match the duration of their deposits better than a 30-year loan. The CU takes less interest-rate risk, and they pass some of those savings to you.
Should You Look Into It?
Not to say the 15/15 ARM is right for everyone. If you’re the type of person who loses sleep over uncertain outcomes in the year 2040, take the 30-Year Fixed. Peace of mind might be worth the extra 20 basis points.
But the 15/15 ARM is worth considering if you’re:
- Buying a “starter home” or condo.
- Planning to upgrade or move in 7-12 years.
- Expecting to refinance when rates drop.
The catch? You’ll probably need to look at credit unions to find one. Which, honestly, is a good thing. The 15/15 ARM is just one example of the kind of product innovation that happens when a lender isn’t trying to flip your mortgage to Wall Street.
Check out our Credit Union Mortgage Dashboard to see who’s offering them in your area.
More on the way
We’re three posts in, and if you’re starting to wonder why some credit unions are able to behave so differently than the big brand banks, then stay tuned. Next post we’re going to talk about the rarest credit union unlock of all: true zero-cost refinancing. Only portfolio lenders can do this, and we’re going to explore what that means.
Be sure to subscribe to the newsletter below to get notified when new posts drop. In the meantime, feel free to catch up on our past posts in the credit union mortgages series:
