What is rebalancing?
- Rebalancing restores your portfolio to your intended asset mix.
- Market drift naturally pushes your allocation off target over time.
- It forces you to sell high and buy low, mechanically.
- Doing it on a set schedule prevents emotional decision-making.
- It keeps your risk at the level you actually chose.
What is rebalancing?
Rebalancing restores your portfolio to your target allocation after markets push the mix off course. Markets create drift, and rebalancing corrects it by trimming winners and adding to laggards, which keeps your risk profile steady over the long term.
Rebalancing is not about maximizing returns. Its purpose is to manage risk, not time the market. You are not chasing winners; you are keeping your risk profile exactly where you decided it should be, for decades at a time.
How often should you rebalance?
A calendar schedule is the simplest. Rebalance once a year, on the same date, so the habit is automatic and easy to keep, and doing it on a fixed schedule prevents emotional decision-making.
A threshold method triggers action only when the mix strays a set amount, say 5% or 10%, which catches big moves sooner. Mechanically you sell the overweight asset and buy the underweight one, which forces you to sell high buy low on autopilot.
The combined method blends both. You set a calendar review, but you only act if the drift has passed a fixed percentage. This keeps you from over-trading small moves while still catching a real imbalance.
Research favors a middle frequency: too frequent means costs and over-trading, too infrequent means the drift grows unchecked. An annual review is the common sweet spot, though what matters most is that you actually stick to the schedule.
What are the costs and limits?
Rebalancing is not free. Every trade can carry costs, and selling winners in a taxable account can trigger capital gains taxes. Move dividends and interest into the underweighted assets first, and let new cash absorb drift, before you sell anything.
The method cannot fix a target that never matched your timeline. But done faithfully, it is forced discipline: it restores your target allocation, removes emotion, and keeps your risk at the level you chose, year after year.
What is the rebalancing bonus?
Rebalancing can add a bonus on top of the risk control. William Bernstein and others showed that a constant-mix strategy, selling what is hot to buy what is cold, can lift returns in a market that swings back and forth. The bonus grows with the swings.
The mechanism is mechanical. Each rebalance forces you to buy low and sell high, and over repeated cycles that harvests gains a buy-and-hold investor never captures. The bonus is largest when two assets swing widely and revert, and it is never guaranteed.
You can rebalance with new money instead of selling. Add contributions to the underweight asset, and take withdrawals from the overweight one. That sidesteps trading costs and taxes while still nudging the mix back to target.
Constant-mix sits alongside buy and hold, constant proportion, and option-based strategies as the four classic allocation approaches. You do not need to master all four. You need to pick one consistently and let the discipline work across every crash and boom.