Mortgage interest rates have recently risen, and are currently very volatile. At the time of this writing, PSECU, my credit union, is offering mortgages at 5.125%, much higher than the 3.125% I locked in at, but lower than the peak above 6% I had recently read about in the news. But what does this mean in practice? Well, let’s run some numbers. Understanding how expensive a house is can be confusing.