<prompt> Human: Quick question for the gurus here.Is active rebalancing of my investment portfolio necessary? Do I have to sell my Winners? Or can I buy in to poor performing funds?Lets say I have a lazy portfolio of funds with one-third Total Stock Market, one-third Total International Market, and one-third Total Bond Market. And lets say that I put in a regular amount of savings in every month. Also assume that I can purchase these funds commission free think ITOT for Fidelity or VTI for Vanguard.Do I actually need to be selling any funds to keep the 1:1:1 ratio? Can I simply just buy more of the poorer performing funds to keep them at 33 of the total portfolio?  <response>: Rebalancing by new contributions is fine. If your winners are too successful so that new contributions are not sufficient to get back to your desired asset allocation, then you are effectively drifting into a different risk profile than you originally set up. If this is acceptable to you, then no additional rebalancing is necessary. If this is not acceptable, then some more active rebalancing is warranted. One good strategy to consider is rebalancing bands, where you take more active rebalancing actions when your allocation has drifted more than 5 away from your intent. Using contributions to even out the ratios otherwise is usually very effective in keeping your portfolio within the selected bands. 