Your Adjustable Rate Mortgage: Blessing or Bomb?

As a loan officer I used to plot several graphs for my clients considering adjustable rate mortgages (ARMs). I’d routinely show them the best case, worst case, and most likely scenarios, and let them decide if they wanted the savings of the ARM or the safety of the fixed loan. If you’re trying to decide whether to keep your ARM today or refinance it, you can perform the same kind of analysis yourself.

First, Look at the Terms of Your ARM

Your paperwork should contain an ARM rider that should give you these pieces of information: Your start rate, your index, your margin, and any rate or adjustment caps and floors. For example, you might have a 3/1 ARM with a start rate of 4%, based on the 1-year LIBOR index, with a margin of 2%, annual adjustments capped at 2%, a lifetime cap of 10%, and a floor of 3%. Your 4% mortgage is set to adjust in a month; what will it do?

Check Your Index

You can find index data on most financial Web sites. The 1-year LIBOR index as of February 2010 is .85158. If your mortgage were adjusting today, you’d add your margin of 2% and get a rate of 2.852%!

Check Your Caps and Floors

But wait, there’s more. Your loan has a floor of 3%, which means that your rate can’t drop below 3% no matter what the LIBOR does. So you’d be at 3%, which isn’t bad. And that 3% is your best case scenario. So what’s your worst-case scenario? Check your caps–your rate can’t increase more than 2% per year. So, if you adjusted to a 3% rate next month, in a year the highest your rate could be go would be to 5%, then the following year to 7%, then 9%, then it would top out at 10% and stay there. So much for worst case.

What’s More Likely?

Best and worst case scenarios are extremes and unlikely to resemble the progress of your actual loan, especially over the long term. But you can predict a more likely and reasonable course for your mortgage. Here’s how: a search of “historical average 1 year LIBOR” online gets me the data I want. I dump it into a spreadsheet and I discover that the average of the 1-year LIBOR since its inception in 1990 is 4.623%. So we can add that to your margin of 2% for a total of 6.623%.

Yes, I could be a statistical stinker and make you calculate the expected value, but an average is a fairly good substitute and no one ever committed suicide trying to calculate an average. It’s a fairly safe bet, then, that your loan will adjust to 3% next month, 5% the following year, and then it may fluctuate around that 6.623% rate over the years–there’s no guaranty, but the longer you have your loan, the more likely it is that your rate will behave itself.

So, Should You Fix Your Interest Rate or Not?

That depends. Fixed rates today are about 5% if you have good credit–less than the average LIBOR ARM rate of 6.623%. You’d probably save money in the long run by refinancing. But what if you’re not in it for the long haul? If this house is a starter, or you have job transfers every five years or so, leaving your ARM alone is probably a safe bet. You know your rate won’t exceed 7% for at least three years.