Try these example inputs in the Rebalancing calculator.
These figures match this guide's worked example. They are illustrative. They stay on this device and never appear in the URL.
Portfolio rebalancing restores a mix you already chose. If one holding grew faster than the other, its weight drifted up. The trade that puts weights back is simple: target weight times the total, minus what you already hold. That is arithmetic, not a view on which name is better.
Key takeaways
Trade = target weight × total value − current value
Total value is the sum of the holdings plus any new cash you type. $6,000 in one name and $4,000 in another, with 50/50 targets, means the first is $1,000 overweight and the second is $1,000 underweight. Buy $1,000 of the second by selling $1,000 of the first.
60% and 40% is a complete mix. 60% and 30% is not. The missing 10% is not filled in, because scaling in silence would change every trade.
Run the same 50/50 example in the rebalancing calculator.
Sometimes the rule is “add cash, do not sell.” New money buys the names that sit below target. Overweights stay put. If the contribution cannot reach every target, leftover demand stays unmet rather than forcing a sale. Leftover cash is shown when every target is already met.
A worked case: $6,000 and $4,000 with 50/50 targets and $1,000 of new cash. The portfolio is then $11,000. A full rebalance would need $1,500 in the second name. Contribution-only buys $1,000 of that name and sells nothing. Ending weights are about 54.55% and 45.45%. The remaining gap is unmet.
If several holdings are underweight and the cash cannot fill every gap, each desired buy is scaled by cash ÷ total unmet demand. The calculator does not pick a favorite name.
A three-holding sketch: targets 40% / 40% / 20%, current values $5,000 / $3,000 / $1,000, and $1,000 of new cash. Total becomes $10,000. Desired buys are $1,000 of the second name and $1,000 of the third. Cash covers half of that $2,000 demand, so each buy is cut in half: $500 and $500. The first name is still overweight and is not sold in contribution-only mode.
That mode does not claim to be better. It is a constraint: no sells.
It sizes the trades that would restore the mix you typed, given today’s values. Drift is a description of the past path, not a forecast.
The calculator can take an optional trading-cost figure. It still does not know about taxes, or whether a name is even tradable. It does not pick targets for you. The $6,000 / $4,000 example above is a two-asset mix you type, not a recommended pair of companies. Try it in the rebalancing calculator.
Rebalancing is also not a return statistic. For a lump-sum path use CAGR; for dated deposits use XIRR. Putting dividends back to work is a different mechanic — see DRIP.
For general education only. Nothing here is investment advice.
Formulas and worked examples are MarketCapLens's. See who checks the numbers.