When and How to Rebalance a Stock Portfolio
Rebalancing brings a portfolio back toward its intended allocation after market moves change the weights. Winners grow into ever-larger slices; laggards shrink. Left alone, a portfolio quietly drifts into a risk profile you never chose. Rebalancing is how you keep your plan — not past price action — in charge.
How drift happens
Start at a target mix. A strong rally in stocks pushes their weight well above target, raising your risk. Rebalancing trims the winner back toward plan.
Three ways to rebalance
| Method | How it works | Trade-off |
|---|---|---|
| Calendar | Check on a schedule (e.g. yearly) and reset to target | Simple; may act when drift is small |
| Threshold | Act only when a weight drifts past a band (e.g. ±5%) | Responsive; needs monitoring |
| Cash-flow | Steer new contributions into underweight areas | Tax-friendly (no selling); slower to correct |
Any of these beats acting on emotion. The point is a repeatable rule.
Worked example: trimming the drift
A $100,000 portfolio targeting 60/40 after a stock rally:
| Sleeve | Target | After rally | Action to reset |
|---|---|---|---|
| Stocks | $60,000 (60%) | $75,000 (75%) | Sell ~$15,000 |
| Bonds / cash | $40,000 (40%) | $25,000 (25%) | Buy ~$15,000 |
You're systematically trimming what ran up and adding to what lagged — the discipline that makes rebalancing valuable, precisely because it feels counterintuitive.
Rebalancing ≠ ignoring fundamentals. If a holding fell because the business deteriorated (not just sentiment), buying more to "rebalance" can throw good money after bad. A broken thesis is an exit decision, not an allocation tweak — see volatility vs. permanent loss.
See it in action: the simulator's Portfolio mode has a Monthly rebalance toggle — turn it on and off to compare how a basket behaves when it's reset to target weights each month versus left to drift.
A portfolio isn't static: markets move, winners compound, and exposures shift. Rebalancing keeps your strategy aligned with your actual goals (and your position-size limits) instead of letting the last rally decide your risk.