If you sign up for a bank purely based on their high-interest savings rate, you should know that it likely won’t last forever. Interest rates fluctuate based on many factors including the Federal Reserve's monetary policy, the economy and competition between banks. Banks can change their interest rates anytime and some do raise or lower them more often than others. They also may have promotional offers for a short period of time. Keep an eye on the interest rates your accounts have, and compare options to make sure you are earning the best return.