Complete Guide to Portfolio Rebalancing
— Timing, Method, Cost, and Taxes
Rebalancing is the work of restoring asset weights that market moves have thrown off back to your target. We systematically cover when, how, and how often to do it, and how to minimize cost and taxes.
Why Is Rebalancing Necessary?
If a portfolio that started at 60% stocks / 40% bonds becomes 75% stocks / 25% bonds after a rally, it's now a riskier portfolio than the risk level you originally set. Leave it unrebalanced and you take a bigger-than-expected loss when the market falls. Risk management is rebalancing's core purpose.
Periodic Rebalancing vs. Band Rebalancing
- Periodic rebalancing: execute on a fixed schedule, 1–2 times a year or 1x a quarter. Simple and easy to keep disciplined.
- Band rebalancing: execute only when an allocation drifts ±5–10%p from target. Cuts trading costs.
Research shows the long-term return difference between the two approaches is minor. If you want simplicity, rebalancing periodically 1x a year fits well. In a highly volatile market, the band approach cuts trading costs.
Rebalancing Without Selling
Instead of selling the overweighted asset, this method directs new capital only into the underweighted asset. You drift toward your target allocation slowly, with no tax or fee impact. Combined with DCA (monthly investing), it becomes a natural form of rebalancing. That said, if the drift is large, selling to rebalance becomes unavoidable.
Tax Considerations
Selling to rebalance overseas stocks triggers a 22% tax on the capital gain. Common approaches include sizing your sale with the annual 250-man-won deduction in mind, or selling a losing position alongside it to offset the gain. Being so afraid of the tax that you postpone rebalancing indefinitely leads to a bigger risk. The feeling that "paying tax is a waste" is exactly what keeps you carrying excess risk.
A Cost-Minimizing Strategy
- Use dividend and interest payments to buy the underweighted asset
- Limit the frequency to 1–2 times a year (frequent trading = accumulating cost and tax)
- Choose a low-fee ETF and brokerage
- Use a tax-advantaged account (like an ISA) where possible
Quarterly Rebalancing — Choosing the Timing and Date
Quarterly rebalancing means checking your portfolio on a set date every 3 months. Fixing it to the calendar — the first Monday of months 1, 4, 7, and 10 (January, April, July, October), for example — lets you keep disciplined rebalancing without an emotional judgment call.
- Timing tips — avoid right after a quarterly earnings release (earnings season), and prefer a high-volume weekday in the middle of the week (Tue/Wed/Thu).
- Fixing the date — "the first week of the quarter" is better than "the last trading day of the quarter" for avoiding year-end tax and volume crowding.
- Combining with a band trigger — a hybrid approach also works well: execute immediately if the drift exceeds ±10%p even before the quarterly date arrives.
Quarterly rebalancing catches drift earlier than 1x a year, which is better for risk management, but it increases the number of trades (cost and tax). The smaller your account, the more efficient it is to cut back to 1–2 times a year.