Guide · Risk Management
What Is Portfolio Rebalancing and Why Winners Get Trimmed
Rebalancing means deliberately selling some of your best performers. It sounds backwards — until you see what happens to a portfolio's risk when nobody ever does it.
Portfolio rebalancing is the practice of periodically buying and selling holdings to bring a portfolio back to its original target allocation — for example, a portfolio built to hold 60% stocks and 40% bonds that has drifted to 75/25 after stocks outperform gets trimmed back toward 60/40 by selling some stocks and buying more bonds.
The drift happens automatically just from different assets growing at different rates, with no action required — which is exactly the problem rebalancing solves. Left untouched, a portfolio's risk profile silently shifts over time: the original 60/40 investor who never rebalances might wake up years later effectively holding an 80/20 portfolio, carrying far more stock-market risk than they ever signed up for, purely because nobody trimmed the winners along the way.
This is also why rebalancing is often described as a disciplined way to 'buy low, sell high' without needing to predict anything — it mechanically sells whatever asset class has become overweight (because it went up) and buys whatever has become underweight (because it lagged), regardless of what either is expected to do next.
Most individual investors rebalance on a fixed schedule (annually, semi-annually) or when an allocation drifts past a set threshold (say, 5 percentage points off target), whichever comes first — a habit that's easiest to build first with a paper portfolio, tracking how allocation drift actually plays out before doing it with a real account.