An Introduction to Portfolio Rebalancing
How a portfolio drifts from its target, and what bringing it back involves.
Portfolio rebalancing is the routine of periodically nudging your holdings back toward a target mix you picked earlier. The idea is simple, but the details — when to do it, and how — are where it gets interesting. This article covers the concept and the common approaches. It's educational reference material, not investment advice.
Why portfolios drift
You usually start with a target allocation — say, a certain percentage in stocks and a certain percentage in bonds — chosen to fit your goals and your comfort with risk. The trouble is that those holdings don't move in step. If stocks climb faster than bonds, the stock slice quietly grows past its target. That gradual slide is what people mean by drift, and it can leave the portfolio carrying more risk, or less, than you signed up for.
How rebalancing works
Rebalancing simply walks the portfolio back toward its target. The usual move is to sell some of whatever has grown past its target and put the proceeds into whatever has fallen below. There's a gentler version, too: steer new contributions toward the underweighted holdings, which shifts the balance without selling anything you already own. Either way, the goal is the same — restore the mix you intended.
Common methods
When to rebalance usually comes down to two approaches. Calendar-based rebalancing means reviewing and adjusting on a fixed schedule, like quarterly or annually. Threshold-based rebalancing means acting only when an allocation drifts past a set percentage from its target. Plenty of people blend the two — checking in on a schedule, but only making a move when drift has actually crossed the threshold.
Considerations
Rebalancing isn't free. It can rack up transaction costs, and selling in a taxable account may trigger taxes, which is why some investors lean on new contributions or rebalance inside tax-advantaged accounts where they can. There's a balance to strike: do it too often and you pay costs without much to show for it; do it too rarely and the portfolio can wander well off its intended risk level. The right cadence really depends on your own situation.
Summary
To sum up: rebalancing is the practice of periodically adjusting holdings to hold a target allocation steady as values shift over time. The common methods are calendar-based and threshold-based, often blended. The aim is to keep a portfolio aligned with the level of risk you intended, while staying mindful of costs and potential taxes along the way.