Along with other decisions you will find yourself making while shopping for a mortgage, you will be deciding whether to take a fixed-rate mortgage (FRM) or an adjustable rate mortgage (ARM).

As the name implies, the interest-rate of an FRM will remain the same throughout the life of the loan. If interest rates are low when you are buying or refinancing a home, an FRM is a good choice, because you can lock in that low interest rate. ARMs, however, will fluctuate as interest rates rise and fall. Your 6 percent rate today could drop to 5 percent next year or end up at 8 percent if the market rate goes up.

Exactly when the rate of your ARM loan will change depends upon the terms of your loan agreement, which could see rates change every three months, once a year, every three years, or not until five years. It’s not uncommon to find ARMs that start at a fixed rate and convert to an adjustable rate after several years.

ARMs also generally come with a "cap," which limits the amount a lender can raise its rate. The cap for most ARMs is 2 percent, meaning a lender can only increase its rate 2 percent within a single adjustment period. But several adjustments can turn a 4 percent interest rate at the beginning of the loan into a 10 percent interest rate later on.