Portfolio Allocation Calculator

Rebalancing a multi-asset crypto portfolio in a spreadsheet works, but it's the kind of thing that compounds errors over time — a wrong target percentage in one row, an outdated price feed in another, and your rebalance is doing the opposite of what you intended.

List your assets, their current holdings, and your target percentages. The calculator computes current allocation versus target, the dollar drift on each position, and the trades required to bring everything back to target. It also flags whether your targets sum to 100 percent (a common spreadsheet bug) and shows the post-rebalance portfolio side by side with the current state.

Useful for periodic rebalancing — quarterly is typical — and for sanity-checking the size of trades before placing them. Doesn't connect to exchanges or place orders; it only does the math.

The math of rebalancing is simpler than it gets credit for. Given current asset values c_i and target weights w_i (summing to 1), total portfolio value V = Σ c_i, target value per asset t_i = V × w_i, drift d_i = c_i − t_i. Positive drift means overweight, sell some; negative drift means underweight, buy more. The calculator surfaces these numbers and the trade list — sell $X of asset A, buy $Y of asset B — that brings drift to zero. What it doesn't handle and shouldn't is the order routing, slippage, and fees of actually executing those trades.

A worked example: a 60/30/10 BTC/ETH/stablecoin portfolio at $100K total. After a rally where BTC outperforms, allocation drifts to 75/20/5. Targets in dollars: $60K BTC, $30K ETH, $10K stablecoin. Current: $75K, $20K, $5K. Trade list: sell $15K BTC, buy $10K ETH, buy $5K stablecoin. Execute, and you're back at target. The number that surprises people is how often this happens — a 15-percentage-point drift in three months is normal in crypto, much less common in equities.

The limitation worth flagging: rebalancing is mechanically right but tax-suboptimal in taxable accounts. Selling appreciated BTC realizes capital gains; if you'd planned to hold long-term and avoid realizing, the rebalance triggers tax. Workarounds: rebalance with new contributions (direct fresh money to underweight assets), rebalance only at year-end with tax-loss harvesting (sell underperforming assets to offset gains elsewhere), or rebalance only in tax-advantaged accounts (IRA, 401(k)) where realization is tax-free. The calculator doesn't model your tax situation — it shows the trades; you pick which ones to actually execute.

For the philosophical question of whether rebalancing helps at all: academic evidence suggests it captures a small "rebalancing bonus" (~0.1–0.5% per year) in volatile markets by mechanically buying low and selling high, but the bonus is sensitive to assumptions and small enough that fees and taxes can eat it. The stronger argument for rebalancing is risk control — without it, your portfolio drifts toward whatever asset performed best, which is often the riskiest. Rebalancing keeps your actual risk close to your stated risk.