Portfolio Rebalance Calculator
Portfolio rebalance calculator
Portfolio total
Targets sum to
Total to move
Largest drift
Enter what each holding is worth now and the weight you want it to have. The table shows the trade that gets you there. Targets must add up to 100% or the result is meaningless — the calculator tells you what yours currently sum to rather than silently normalising them. Fees, spreads and any tax event from selling are not modelled, and they are often the reason rebalancing less often is the better answer. Runs entirely in your browser. Not advice.
What this calculator does
You give it the current value of up to four holdings and the percentage weight you want each to have. It returns each holding’s current weight, its target value, and the buy or sell that would get it there — plus the total amount that has to change hands and your largest single drift in percentage points.
How to read the output
Current % is what the position has become, which after any period of divergent performance is rarely what you chose. Trade is the amount to buy or sell. Total to move is the value that changes hands once — the sells and the buys are the same amount, so it is counted once, not twice. Largest drift is the biggest gap in percentage points between a current and a target weight, which is the usual trigger for deciding a rebalance is due at all.
Targets that do not sum to 100%
If your targets add up to something other than 100%, the calculator says so and shows you the sum rather than quietly normalising it. Silently rescaling your inputs would produce target values that look authoritative and mean nothing. A sum of 90% means you have not told it where the last 10% goes; a sum of 110% means the plan does not fit the portfolio.
The costs this ignores, which are the reason not to rebalance often
Fees, spreads and slippage on every trade are not modelled. Neither is tax: in many jurisdictions selling to rebalance is a disposal and creates a taxable event even though your total holdings did not change. This is why rebalancing on a schedule regardless of drift, or on a very tight drift threshold, is frequently worse than doing it rarely — the transaction and tax drag can exceed the benefit of precise weights. The calculator gives you the trades; deciding whether they are worth making is your call and depends on numbers only you have.
Frequently asked questions
Can I use fewer than four assets? Yes. Leave the unused rows at zero for both value and target and they are omitted from the table.
How do I add to a portfolio instead of selling? Increase the value of the underweight holding by the amount you plan to contribute and re-read the table. Rebalancing with new money avoids the disposals entirely.
Why is “total to move” half the sum of the trades? Because every dollar sold is a dollar bought. Counting both would double it.
Is this advice? No. See our disclaimer.