Rebalancing means trimming the part of your mix that grew too big and topping up the part that shrank, to get back to the split you originally chose.
A mix left alone drifts as the fastest-growing part keeps growing, quietly taking on more risk than you originally chose, without you deciding that on purpose.
Start 50% shares, 50% bonds. Shares double, bonds stay flat: now it's about 67% shares, 33% bonds. Rebalancing sells some shares and buys bonds to get back to 50/50.
Rebalancing means selling the thing that's been rising, which feels wrong in the moment. It is not about predicting the future; it's about keeping the risk you originally chose.
Compare your current mix with your original plan once or twice a year. A gap of more than a few points is usually worth correcting.
Rebalancing keeps the risk you chose, by trimming what grew and topping up what shrank.
Compare your mix with your plan.