ianalloway Portfolio Rebalancer
Calculate the exact trades needed to rebalance any portfolio back to target allocations. Works with stocks, crypto, ETFs, or any mix of assets.
Quick Rebalance
Simple portfolio rebalance
python3 -c "
def rebalance(holdings, targets, prices=None):
'''
holdings: dict of {asset: quantity}
targets: dict of {asset: target_pct} (must sum to 1.0)
prices: dict of {asset: price_per_unit} (optional, defaults to 1.0)
'''
if prices is None:
prices = {a: 1.0 for a in holdings}
current_values = {a: holdings.get(a, 0) * prices.get(a, 1) for a in targets}
total = sum(current_values.values())
if total <= 0:
print('Portfolio value is zero or negative.')
return
print(f'Total Portfolio Value: \${total:,.2f}')
print(f'{\"\":-<60}')
print(f'{\"Asset\":<12} {\"Current\":>10} {\"Target\":>10} {\"Diff\":>10} {\"Trade\":>14}')
print(f'{\"\":-<60}')
for asset in sorted(targets.keys()):
current_pct = current_values[asset] / total
target_pct = targets[asset]
diff_pct = target_pct - current_pct
trade_value = diff_pct * total
trade_qty = trade_value / prices.get(asset, 1)
action = 'BUY' if trade_value > 0 else 'SELL'
if abs(trade_value) < 0.01:
action = ' OK'
print(f'{asset:<12} {current_pct:>9.1%} {target_pct:>9.1%} {diff_pct:>+9.1%} {\"balanced\":>14}')
else:
print(f'{asset:<12} {current_pct:>9.1%} {target_pct:>9.1%} {diff_pct:>+9.1%} {action} {abs(trade_qty):>7.4f}')
# Example: Crypto portfolio
holdings = {'BTC': 0.5, 'ETH': 4.0, 'SOL': 100}
targets = {'BTC': 0.50, 'ETH': 0.30, 'SOL': 0.20}
prices = {'BTC': 95000, 'ETH': 3200, 'SOL': 180}
rebalance(holdings, targets, prices)
"
Rebalance with new deposit
python3 -c "
def rebalance_with_deposit(holdings, targets, prices, deposit=0):
current_values = {a: holdings.get(a, 0) * prices.get(a, 1) for a in targets}
total = sum(current_values.values()) + deposit
print(f'Current Value: \${sum(current_values.values()):,.2f}')
print(f'New Deposit: \${deposit:,.2f}')
print(f'New Total: \${total:,.2f}')
print(f'{\"\":-<65}')
print(f'{\"Asset\":<10} {\"Now\":>10} {\"Target\":>10} {\"Action\":>8} {\"Qty\":>10} {\"Value\":>12}')
print(f'{\"\":-<65}')
for asset in sorted(targets.keys()):
target_value = targets[asset] * total
current_value = current_values.get(asset, 0)
diff = target_value - current_value
qty = diff / prices[asset]
action = 'BUY' if diff > 0 else 'SELL' if diff < 0 else 'HOLD'
pct_now = current_value / (total - deposit) * 100 if (total - deposit) > 0 else 0
print(f'{asset:<10} {pct_now:>9.1f}% {targets[asset]*100:>9.1f}% {action:>8} {qty:>+10.4f} \${abs(diff):>10,.2f}')
# Example: Add \$5000 to a stock portfolio
holdings = {'VTI': 50, 'VXUS': 20, 'BND': 30, 'VTIP': 10}
targets = {'VTI': 0.50, 'VXUS': 0.20, 'BND': 0.20, 'VTIP': 0.10}
prices = {'VTI': 280, 'VXUS': 60, 'BND': 72, 'VTIP': 50}
rebalance_with_deposit(holdings, targets, prices, deposit=5000)
"
Drift Detection
Check if portfolio needs rebalancing
python3 -c "
def check_drift(holdings, targets, prices, threshold=0.05):
'''Check if any asset has drifted beyond threshold from target.'''
values = {a: holdings.get(a, 0) * prices.get(a, 1) for a in targets}
total = sum(values.values())
needs_rebalance = False
print(f'Portfolio: \${total:,.2f} | Drift Threshold: {threshold:.0%}')
print(f'{\"\":-<50}')
for asset in sorted(targets.keys()):
pct = values[asset] / total if total > 0 else 0
drift = abs(pct - targets[asset])
flag = ' ** REBALANCE' if drift > threshold else ''
if drift > threshold:
needs_rebalance = True
print(f'{asset:<10} {pct:>8.1%} vs {targets[asset]:>6.1%} drift: {drift:>5.1%}{flag}')
print(f'{\"\":-<50}')
if needs_rebalance:
print('ACTION NEEDED: Portfolio has drifted beyond threshold.')
else:
print('Portfolio is within tolerance. No action needed.')
# Example
holdings = {'BTC': 0.8, 'ETH': 5.0, 'SOL': 50}
targets = {'BTC': 0.50, 'ETH': 0.30, 'SOL': 0.20}
prices = {'BTC': 97000, 'ETH': 3100, 'SOL': 175}
check_drift(holdings, targets, prices, threshold=0.05)
"
Tax-Aware Rebalancing
Minimize sells (buy-only rebalance using new cash)
python3 -c "
def buy_only_rebalance(holdings, targets, prices, cash):
'''Rebalance by only buying - never selling (tax-efficient).'''
values = {a: holdings.get(a, 0) * prices.get(a, 1) for a in targets}
total = sum(values.values()) + cash
print(f'Available Cash: \${cash:,.2f}')
print(f'Post-Rebalance Total: \${total:,.2f}')
print(f'{\"\":-<50}')
buys = {}
for asset in targets:
target_value = targets[asset] * total
current_value = values.get(asset, 0)
deficit = max(0, target_value - current_value)
buys[asset] = deficit
buy_total = sum(buys.values())
if buy_total > cash:
scale = cash / buy_total
buys = {a: v * scale for a, v in buys.items()}
remaining = cash
for asset in sorted(buys.keys(), key=lambda a: buys[a], reverse=True):
buy_val = min(buys[asset], remaining)
qty = buy_val / prices[asset]
if buy_val > 0.01:
print(f'BUY {qty:.4f} {asset:<8} (\${buy_val:,.2f})')
remaining -= buy_val
if remaining > 0.01:
print(f'Remaining cash: \${remaining:,.2f}')
holdings = {'VTI': 100, 'VXUS': 30, 'BND': 40}
targets = {'VTI': 0.60, 'VXUS': 0.25, 'BND': 0.15}
prices = {'VTI': 280, 'VXUS': 60, 'BND': 72}
buy_only_rebalance(holdings, targets, prices, cash=3000)
"
Tips
- Rebalance on a schedule (quarterly or when drift exceeds 5%)
- Use new deposits to rebalance before selling (tax-efficient)
- Consider transaction costs - skip tiny trades under $50
- Keep target allocations simple - fewer assets = easier to maintain
- Document your target allocation and the reasoning behind it
Common Allocations
| Strategy | Stocks | Bonds | Crypto | Real Estate |
|---|---|---|---|---|
| Aggressive Growth | 80% | 5% | 10% | 5% |
| Balanced | 60% | 25% | 5% | 10% |
| Conservative | 40% | 45% | 0% | 15% |
| Crypto-Heavy | 30% | 10% | 50% | 10% |
Author
Created by Ian Alloway - Data Scientist specializing in AI/ML and portfolio optimization.
License
MIT License