Using stable short-term, tax-free municipal bond funds to beat the bank?
Banks' savings interest is ridiculous, has always been, compared to other investment options. But there's a reason for that: its safe. You will get your money back, and the interest on it, as long as you're within the FDIC insurance limits. If you want to get more returns - you've got to take more risks. For example, that a locality you're borrowing money to will default. Has happened before, a whole county defaulted. But if you understand the risks - your calculations are correct.