<prompt> Human: I have a 401k through my employer that by default puts all contributions into a Fidelity Target Retirement fund with an expense ratio of .65. However, Fidelity offers a range of mutual funds, including total stock market, total international stock market, and total bond market index funds through Vanguard, with their much lower expense ratios .035, .11, .05.I was thinking of changing my contributions to just buy the appropriate proportion of these three funds, with a plan to rebalance annually and change the stockbond ratio appropriately as the years go on. I would effectively mimic a VanguardFidelity target retirement fund.Is there any reason not to do this? Long-term I would expect the returns to be comparable but the savings in fees to be substantial.Thanks in advance.  <response>: So yes, you should do this and there is no reason not to. 