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Why Rebalancing Matters
Portfolio allocations drift as assets grow at different rates:
Original allocation: 70% stocks, 30% bonds
After 5 years (stocks up 50%, bonds up 10%):
- Stocks: $175,000 (was $70,000)
- Bonds: $33,000 (was $30,000)
- Total: $208,000
- New allocation: 84% stocks, 16% bonds
Your portfolio is now too aggressive. If a market crash occurs, losses will be larger than intended. Rebalancing returns it to 70/30.
How Rebalancing Works
Step 1: Calculate current allocation
- Stocks: 84% of $208,000 = $174,720
- Bonds: 16% of $208,000 = $33,280
Step 2: Calculate target allocation
- Stocks target: 70% of $208,000 = $145,600
- Bonds target: 30% of $208,000 = $62,400
Step 3: Rebalance
- Sell $29,120 of stocks
- Buy $29,120 of bonds
Result: Back to 70/30 allocation
Rebalancing Frequency
Monthly: Too frequent; wastes money on transaction costs
Quarterly: Still too frequent for most investors
Annually: Optimal balance; captures significant allocation drift without excessive costs
As-needed (threshold-based): Rebalance only when allocation drifts >5% from target
Example: If target is 70/30 and allocation becomes 75/25, rebalance. If it becomes 71/29, don't (drift is minor).
The Emotional Benefit
Rebalancing forces contrarian behavior:
In 2020 (bull market):
- Stocks were booming
- Emotions: "Buy more stocks!"
- Rebalancing: "Sell some stocks; buy bonds"
- Timing: Sell near the top (good)
In 2022 (bear market):
- Stocks were crashing
- Emotions: "Sell everything!"
- Rebalancing: "Sell some bonds; buy stocks"
- Timing: Buy near the bottom (good)
Rebalancing mechanically forces you to do the opposite of what emotions recommend—buying low, selling high.
Returns Impact
On a $1 million portfolio:
- 0.15% improvement = $1,500/year
- Over 30 years at compound growth: $100,000+ in extra wealth
This isn't a large improvement, but it's reliable and comes from disciplined behavior (not complex strategies).
Tax Implications
In taxable accounts: Rebalancing creates capital gains (selling appreciated assets = taxable event)
Strategy: Rebalance by directing new money to underweighted assets (buying bonds instead of stocks) rather than selling stocks.
In retirement accounts (401k, IRA): No tax consequences for rebalancing; you can freely sell and buy without tax impact.
This is one reason retirement accounts are superior—you can rebalance without tax friction.
Automatic Rebalancing Strategies
1. New money direction
- Target 70/30
- Allocation drifts to 75/25
- New $10,000 contribution goes entirely to bonds (25% of $40,000 = $10,000 in bonds)
- Gradually returns to 70/30
2. Target-date funds
- Automatically rebalance internally
- No action required
- 0.03-0.15% expense ratio
3. Automated rebalancing
- Many brokers offer automatic rebalancing
- Set it and forget it
- Rebalances quarterly or annually
Rebalancing During Crises
Rebalancing is most valuable during crises, but most psychologically difficult:
2008 financial crisis:
- Stocks down 50%
- Investors who rebalanced (selling bonds, buying stocks at 50% discount) prospered
- Investors who panicked and sold everything suffered
Benefit of rebalancing: It forces you to have a plan before emotions take over. You've already decided: "If stocks crash, I'll buy." When they crash, you execute the plan.
Rebalancing Costs
Transaction costs: Minimal with modern brokers ($0 trading commissions)
Tax costs: Can be significant in taxable accounts if rebalancing creates gains
Spread costs: Selling and buying creates bid-ask spreads (usually 0.01-0.05% for stocks)
Total costs are typically <0.2%, so annual rebalancing paying 0.2% cost to gain 0.15% return is roughly break-even (but improves discipline, which has value).
Rules of Thumb
Simple approach:
- Rebalance annually on a fixed date (e.g., January 1)
- Set and forget
- No complex calculations
Threshold approach:
- Set tolerance bands (e.g., 70% ±5% = 65-75%)
- Monitor allocations quarterly
- Rebalance only when drifting outside bands
- Reduces unnecessary trading
Rebalancing a 3-Fund Portfolio
Target allocation:
- 50% VTI (U.S. stocks)
- 30% VXUS (International)
- 20% BND (Bonds)
Annual rebalancing:
- Calculate current dollar amounts and percentages
- Determine how much to buy/sell to return to 50/30/20
- Execute trades
- Done for the year
Simple, disciplined, and effective.
The Bottom Line
Rebalancing is not exciting, but it's mathematically sound and psychologically valuable. It forces discipline, improves returns slightly, and ensures you maintain your target risk level.
The best portfolio isn't the one with the highest return—it's the one you'll stick with during crashes. Rebalancing helps ensure you stick with your plan when emotions run high.
