text: Never, when interest rates go down, your mortgage will not.  When they go up your rate will go up.  I am not sure why that person said an arm may be a good idea.\n\nPeople who opt for mortgages other than fixed either have bad credit or don't know any better.  The mortgage company's get you hooked by giving you a rate of 1% the first year and then it increases.  Arms give you an extremely low rate then jump up extremely high to make up for those years.  They assume you will have more money and be in a better financial position.  Your best bet for any mortgage if you have good credit is fixed with the going rate at the current time.