Portfolio Rebalancer | Target Allocation & Drift Analysis
Rebalance your investment portfolio to target allocations. Analyze drift, generate buy/sell trade recommendations, and model cash additions. Supports up to 15 assets with a visual allocation chart and tax-lot awareness.
Assets (3/15)
Target sum: 100.0% ✓Optional. Added before rebalancing.
Only trade if drift exceeds this.
Enter to calculate · Esc to reset
What Is the Portfolio Rebalancer | Target Allocation & Drift Analysis?
Portfolio rebalancing is the process of buying and selling assets to restore your target allocation after market drift has changed your weightings. This tool calculates exactly how much to buy or sell of each holding, supports adding new cash before rebalancing, and provides a drift score so you can measure portfolio health at a glance.
- ›Drift analysis for up to 15 assets, see exactly how far each position has moved from its target as a percentage point deviation.
- ›New cash deployment, add a lump sum before calculating; the tool allocates new money toward under-weight positions first to minimize selling.
- ›Drift threshold, set a minimum deviation (e.g., 5%) below which positions are marked HOLD to avoid unnecessary tax events and transaction costs.
- ›RMS Drift Score, root-mean-square drift gives a single number representing overall portfolio misalignment. A score under 2 is excellent; above 8 warrants rebalancing.
- ›Visual allocation bars, see current vs target allocation for every asset at a glance, color-coded for instant pattern recognition.
Formula
Target Value per Asset
Target Value = Total Portfolio × (Target % / 100)
Trade Amount
Trade = Target Value − Current Value
Positive → BUY | Negative → SELL | ~0 → HOLD
Drift (Absolute)
Drift = Current % − Target %
Drift Score (Portfolio Health)
RMS Drift = √( Σ(Driftᵢ²) / n )
Root-mean-square of all individual drifts. Lower is better.
With New Cash
Total = Current Portfolio Value + New Cash
New cash is distributed proportionally toward targets before trades are calculated.
Drift Threshold — Why It Matters
Threshold = 0% → Rebalance to exact targets (maximum precision, maximum trades)
Threshold = 5% → Only trade when drift exceeds 5 percentage points (reduces churn)
Threshold = 10% → Wide tolerance, minimal trades (suitable for taxable accounts)
How to Use
- 1
Enter each asset with its name, target allocation percentage, and current market value.
- 2
Optionally enter new cash to deploy before rebalancing.
- 3
Set a drift threshold — assets within this tolerance are marked HOLD.
- 4
Click Rebalance to see buy/sell trade recommendations, allocation bars, and drift score.
- 5
Execute the recommended trades through your broker.
- 1Enter your assets: Add each holding with a name, target allocation percentage, and current market value in dollars. Targets must sum to exactly 100%.
- 2Add new cash (optional): If you have fresh money to invest, enter it in the "New Cash" field. It is added to the total before rebalancing trades are calculated.
- 3Set drift threshold: Enter the minimum drift (in percentage points) to trigger a trade. Use 0 for exact rebalancing or 5–10 for tax-efficient rebalancing.
- 4Click Rebalance: The tool shows buy/sell amounts for each asset, summary cards, visual allocation bars, and the full trade table.
- 5Execute trades: Use the trade amounts as guidance when placing orders with your broker. HOLD positions require no action.
Example Calculation
Example: 3-asset portfolio, $5,000 new cash, 5% threshold
Current holdings:
US Stocks (VTI) — Target: 60% — Current: $42,000
Intl Stocks (VXUS) — Target: 25% — Current: $14,000
Bonds (BND) — Target: 15% — Current: $14,000
New cash: $5,000
Total portfolio: $75,000 | Threshold: 5%
Current %: VTI 60.0% | VXUS 20.0% | BND 20.0%
Drift: VTI 0.0% | VXUS −5.0% | BND +5.0%
Target values: VTI $45,000 | VXUS $18,750 | BND $11,250
Trades: BUY VXUS $4,750 · SELL BND $2,750 · VTI HOLD
RMS Drift Score = √((0² + 5² + 5²) / 3) = 4.08%
Understanding Portfolio Rebalancer | Target Allocation & Drift Analysis
Why Portfolios Drift
Every portfolio drifts away from its target allocation over time because different asset classes deliver different returns. A portfolio starting at 60% stocks and 40% bonds will drift to perhaps 70% stocks and 30% bonds after a strong equity run. This is not a problem in the short term, but over years it changes your risk profile meaningfully: a portfolio that was designed for moderate risk gradually becomes an aggressive portfolio, often without the investor noticing.
The Cost of Not Rebalancing
Drifting allocation concentrates risk in whatever performed best recently — which historically is often a contrarian signal. Many investors who never rebalanced in the late 1990s found their tech-heavy portfolios dramatically over-weight in technology just before the dot-com crash. The portfolio had doubled in tech weight through appreciation, not intention.
- ›Increased volatility: over-weight equities mean larger drawdowns in bear markets.
- ›Sequence-of-returns risk: retirees drawing income from an un-rebalanced portfolio face amplified damage in down years.
- ›Behavioral drift: portfolios that look nothing like the original plan are harder to hold through volatility.
Rebalancing Methods Compared
| Method | How It Works | Best For |
|---|---|---|
| Calendar | Rebalance on a fixed schedule (quarterly, annually) | Simple rule-based investors |
| Threshold | Only rebalance when drift exceeds a set %, e.g. 5% | Taxable accounts, cost-conscious |
| Cash Flow | Direct new contributions to under-weight assets | Regular savers, tax efficiency |
| Hybrid | Calendar check + threshold trigger | Most retail investors |
The Case for a Simple Three-Fund Portfolio
Many long-term investors find that three broad index funds cover the entire investable market with minimal overlap and maximum diversification. A classic allocation is US total market, international total market, and US bonds. Rebalancing such a portfolio once per year takes under five minutes and captures the full benefit of disciplined allocation without excessive complexity.
Frequently Asked Questions
How often should I rebalance my portfolio?
Most investors rebalance once or twice per year, or when drift exceeds 5–10 percentage points.
- ›Calendar rebalancing (e.g., every January 1) is simple and predictable.
- ›Threshold-based rebalancing (only act when drift exceeds a set %) generates fewer trades.
- ›In taxable accounts, fewer trades mean fewer taxable events — use a wider threshold (5–10%).
- ›In tax-advantaged accounts (IRA, 401k), rebalance aggressively without worrying about taxes.
- ›Using new contributions to buy under-weight assets lets you rebalance without selling anything.
What is the RMS Drift Score?
RMS Drift = √(Σ(Driftᵢ²) / n). It squares each asset's drift before averaging, so large deviations count more than small ones.
- ›Score under 2%: well-balanced portfolio.
- ›Score 2–5%: minor drift, acceptable for most investors.
- ›Score 5–8%: meaningful drift, consider rebalancing soon.
- ›Score above 8%: significant misalignment, rebalancing recommended.
A single asset drifting 15% will inflate the score more than three assets each drifting 5%, which is the intended behavior since concentrated drift is more dangerous.
What is the drift threshold and how should I set it?
The threshold filters out small drifts to reduce unnecessary trading and tax events.
- ›0%: exact rebalancing. Every asset is traded to hit its precise target.
- ›5%: the most common setting. Only trade when drift is meaningful.
- ›10%: wide tolerance. Best for taxable accounts to minimize capital gains.
- ›Use new cash contributions to reduce drift passively before selling anything.
How does the new cash deployment work?
New cash is added to the total portfolio before targets are calculated. This makes under-weight positions receive larger buy recommendations, reducing the need to sell.
- ›This is called "cash flow rebalancing" — very tax-efficient.
- ›Ideal for accounts where you make regular contributions (e.g., 401k, IRA).
- ›Eliminates capital gains on the assets you would otherwise need to sell.
- ›Works best when the new cash is large enough to cover at least some of the under-weight deficit.
Does this calculator account for taxes on selling?
Trade amounts shown are gross figures. After-tax proceeds depend on your cost basis and tax situation.
- ›Short-term capital gains (held under 1 year): taxed as ordinary income.
- ›Long-term capital gains (held over 1 year): typically 0%, 15%, or 20% in the US.
- ›Tax-loss harvesting: selling losing positions can offset gains elsewhere.
- ›In IRAs and 401(k)s: no capital gains, rebalance freely.
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