Portfolio Rebalancing Calculator

Portfolio Inputs

Total Portfolio Value

Current total portfolio value

Asset Allocations

Asset Target % Current % Corridor (pp) TC Rate %

Asset

Target %

Current %

Corridor (pp)

TC Rate %

Asset

Target %

Current %

Corridor (pp)

TC Rate %

Asset

Target %

Current %

Corridor (pp)

TC Rate %

Asset

Target %

Current %

Corridor (pp)

TC Rate %

Target weights sum: 100.0% Current weights sum: 100.0%

Corridor Rebalancing

Status = "Within" if Lower < Current < Upper

Lower = Target - Corridor | Upper = Target + Corridor
Corridor width is in percentage points (e.g., 5 pp around a 60% target = [55%, 65%]).
At boundary = Outside (conservative convention). If any asset breaches, all assets reset to targets.

Calculator by Ryan O'Connell, CFA

Rebalancing Analysis

Total Drift 0.00%

Outside Corridor 0

Est. Rebalancing Cost $0.00

Turnover 0.00%

Analyzing...

Asset	Drift	Corridor	Status	Trade	Cost

Formula Breakdown

Drift = Current Weight - Target Weight

Trade = (Target - Current) / 100 × Portfolio Value

Model Assumptions

If any asset breaches its corridor, all assets are fully reset to target weights
Strict inequality: weight exactly at the corridor boundary is treated as Outside (a conservative convention)
Corridor widths are in percentage points, not percent of target
Rebalancing is instantaneous (no market impact modeled)
Transaction costs are symmetric (same for buy and sell)
Trades execute at current market prices; no tax consequences modeled
Corridor widths are user-defined; optimal width depends on: transaction costs (+), risk tolerance (+), correlation with rest of portfolio (+), asset volatility (-)

For educational purposes. Not financial advice. Market conventions simplified.

Understanding Portfolio Rebalancing

What is Portfolio Rebalancing?

Portfolio rebalancing is the process of realigning asset weights back to their strategic target allocations. As markets move, actual portfolio weights drift from targets, potentially changing the portfolio's risk-return profile. Rebalancing restores the intended allocation through buying and selling.

Key Formulas

Drift: Current Weight - Target Weight
Corridor: [Target - Width, Target + Width]
Trade: (Target - Current) / 100 × Portfolio Value
At corridor boundary: triggers rebalancing (strict inequality)

Rebalancing Approaches

Calendar Rebalancing

Fixed schedule
Rebalance at predetermined intervals (monthly, quarterly, annually). Simple to implement but may trade when unnecessary.

Threshold (Corridor) Rebalancing

Drift-based triggers
Rebalance only when weights breach corridor bands. More cost-efficient but requires continuous monitoring.

Optimal Corridor Width Factors

According to the CFA Institute curriculum (MTMP Chapter 11), optimal corridor width depends on:

Transaction costs (+): Higher costs favor wider corridors to avoid unnecessary trading
Risk tolerance (+): Higher tolerance allows wider corridors
Correlation (+): Higher correlation with the rest of the portfolio favors wider corridors
Asset volatility (-): Higher volatility favors narrower corridors to control risk

Tip: You can use cash flows (new contributions or withdrawals) to rebalance without incurring additional transaction costs. This is particularly useful in taxable accounts where selling appreciated assets triggers capital gains taxes.

Frequently Asked Questions

Portfolio rebalancing is the process of realigning asset weights in a portfolio back to their target allocations. Over time, market movements cause actual weights to drift from targets. Rebalancing is important because it maintains the portfolio's intended risk-return profile, prevents unintended concentration in assets that have appreciated, and enforces a disciplined "buy low, sell high" approach by selling winners and buying underperformers.

A rebalancing corridor (also called a band or threshold) defines the allowable range around each asset's target weight. If the current weight moves outside the corridor, rebalancing is triggered. According to the CFA Institute curriculum, optimal corridor width depends on four factors: higher transaction costs favor wider corridors, higher risk tolerance favors wider corridors, higher correlation with the rest of the portfolio favors wider corridors, and higher asset volatility favors narrower corridors. Typical corridors range from 3% to 10% depending on the asset class.

There are two main approaches: calendar rebalancing (rebalancing at fixed intervals like monthly or quarterly) and threshold rebalancing (rebalancing only when weights drift beyond predetermined corridors). Academic research and the CFA curriculum suggest that threshold-based rebalancing tends to be more cost-efficient because it avoids unnecessary trades when drift is small, though results depend on market conditions. A common practical approach combines both: check weights periodically but only rebalance when corridors are breached.

Rebalancing involves transaction costs (commissions, bid-ask spreads) and potential tax consequences from realizing capital gains. In taxable accounts, selling appreciated assets triggers capital gains taxes. Strategies to minimize these costs include using cash flows (new contributions or withdrawals) to rebalance, rebalancing in tax-advantaged accounts first, tax-loss harvesting to offset gains, and setting wider corridors to reduce trading frequency.

Enter your portfolio value, target and current weights for each asset class, corridor widths, and transaction cost rates. The calculator computes drift (current minus target weight), checks whether each asset's current weight falls within its corridor band using strict inequality, and determines whether rebalancing is triggered. If any asset breaches its corridor, the calculator shows the trades needed to fully reset all assets to their target weights and estimates the associated transaction costs. Use the companion article for rebalancing policy guidance; use this calculator for the live math.

Rebalancing can have a modest impact on long-term returns. It systematically sells assets that have risen above their targets and buys those that have fallen below, which may add a "rebalancing bonus" in mean-reverting markets. However, in strongly trending markets, rebalancing can reduce returns by selling winners too early. The primary benefit of rebalancing is risk management rather than return enhancement — it keeps the portfolio aligned with the investor's risk tolerance and strategic objectives.

Disclaimer

This calculator is for educational purposes only. Actual rebalancing decisions should consider transaction costs, tax implications, liquidity constraints, and your specific investment objectives. Consult a qualified financial advisor before making portfolio changes.