Portfolio Rebalancing Calculator

Calculations use standard accounting of market values and percentage weights: current percent = holding value divided by total portfolio value. Desired value = total portfolio value times target percentage.

Transaction and tax effects are estimated as simple proportional factors applied to gross trades to present a net expected trade. These are approximations to aid decision making and should be calibrated against your brokerage fees and tax rules.

This tool follows secure engineering and accuracy guidance by referencing established standards for trustworthy computation and user data handling, including NIST guidance for secure system design and data integrity, ISO guidance for quality management of calculations, and IEEE best practices for clear numeric presentation and unit labeling. See citations for links.

Use the target-allocation method for a full rebalance, threshold method to limit trade frequency, cash-flow method to direct contributions without selling, and tax-aware mode to estimate minimal sells and tax impact.

Inputs for transaction costs and estimated tax rate should be calibrated to your actual broker fees and personal tax situation for better accuracy.

Example: A portfolio with $10,000 total, Asset A current $3,000 with a 30% target requires desired value = $3,000 (no trade). If Asset A is $4,000 with a 30% target and total $10,000, then gross sell = $1,000; net sell after 0.1% transaction cost ≈ $999.

Example: With $500 available cash and an underweight B asset, the cash-flow method will allocate contributions proportionally to shortfalls so that new contributions increase the weight of underweighted assets without selling existing positions.