Free Stock Portfolio Calculators
A portfolio drifts into a shape nobody chose
Four calculators for the questions that arrive after the buying decisions: what has drifted, what the account actually earned as opposed to received, how concentrated it really is, and what adding to a loser would do.
Portfolio Rebalancing Calculator
Compare current weights against targets and get the buy and sell amounts that restore them, including a new contribution.
Result
Largest drift
Equities
- Largest drift
- 8%
- Current total
- $100,000
- Total after contribution
- $100,000
- Contribution
- $0
- Total to buy
- $8,000
- Total to sell
- $8,000
- Targets sum to
- 100%
- Targets check
- Targets sum to 100%
This tool is for informational and educational purposes only. It is not financial or investment advice, and past performance does not guarantee future results.
Adding new money to the under-weight assets rebalances without selling, which avoids transaction costs and any tax event a sale would create.
Rebalancing is a discipline, not a return strategy. Set a drift threshold or a schedule and follow it.
Rebalancing plan
| Asset | Current value | Current % | Target % | Target value | Buy / (sell) |
|---|---|---|---|---|---|
| Equities | $68,000 | 68% | 60% | $60,000 | -$8,000 |
| Bonds | $18,000 | 18% | 25% | $25,000 | $7,000 |
| Property | $9,000 | 9% | 10% | $10,000 | $1,000 |
| Cash | $5,000 | 5% | 5% | $5,000 | $0 |
Read the full guide, worked examples and FAQ for this calculator →
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Portfolio Rebalancing Calculator
Compare current weights against targets and get the buy and sell amounts that restore them, including a new contribution.
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Position Concentration Calculator
Measure how concentrated a portfolio really is: weights, the top three, a concentration index and the effective number of holdings.
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Averaging Down Calculator
See the new average price after adding to a losing position, and how much the move to break even actually shortens.
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Portfolios are usually built deliberately and maintained by default. The holdings that perform become a larger share of the total, the allocation stops resembling the one chosen, and the reported return quietly includes every deposit made along the way.
These tools address that maintenance layer. None of them suggests an allocation, an asset or a strategy - they measure what a portfolio has become and calculate what specific adjustments would do.
Browse by category
Portfolio
Cost basis, allocation, profit and rebalancing.
Why use StockPortfolioTools
Rebalance with new money first
Directing a contribution at the underweight holdings restores targets without selling, which avoids transaction costs and realised gains.
Return, not deposits
Fifty thousand to seventy thousand after eighteen thousand of deposits is a two thousand gain. It is the most common error in self-reported returns.
Effective holdings, not the count
Twenty positions where one is half the value behaves like three or four. The concentration index makes that visible.
Averaging down, both sides shown
A lower average and a shorter path to break even, against more capital committed to an idea that has been wrong so far.
How it works
- Measure concentration before deciding whether the allocation needs attention.
- Rebalance with contributions where possible rather than by selling.
- Calculate the return with contributions removed, over the period actually held.
- Before adding to a losing position, run the numbers and apply the honest test.
Frequently asked questions
How often should I rebalance?
This site does not suggest a frequency. Schedule-based and threshold-based approaches are both common, and the right one depends on transaction costs, tax treatment and the portfolio itself.
Why does my return look lower here than in my broker app?
Because contributions are removed. Many account summaries report the change in value, which credits the investments with every deposit made during the period.
Does counting holdings measure diversification?
No. Weights matter more than the count, and holdings that move together concentrate risk in a way no value-based calculation can detect.
Is averaging down a bad idea?
It depends on the position and the plan behind it. The calculator shows both sides - the lower average and the larger commitment - and takes no view on any particular case.
Is any of this investment advice?
No. These are calculators, for informational and educational purposes only. They recommend no asset, allocation or strategy, and nothing you enter leaves your browser.