Portfolio Rebalancing Calculator
Calculate how much to buy or sell to rebalance your investment portfolio.
What this calculator does
This calculator tells you exactly what to buy and sell to return a drifted portfolio to its target allocation. Enter your total portfolio value along with your current and target percentages for stocks, bonds, and cash, and it returns the dollar adjustment needed in each — positive to buy, negative to sell.
The conversion from percentages to dollars is the whole value. Knowing you are 12 percentage points overweight in stocks is abstract; knowing you need to sell $30,000 of stocks and buy $25,000 of bonds is an instruction you can act on this afternoon.
When to use it
Use it at your scheduled rebalancing review — annually for most people, or whenever an allocation drifts more than 5 percentage points from its target. After a strong year for stocks or a sharp market fall are the two moments the drift is usually largest and the discipline hardest to follow.
It is also the tool for implementing a deliberate change in strategy, such as shifting from 70/30 to 60/40 as retirement approaches. And it works in reverse as a planning check: if the required trades would trigger a large taxable gain, that is a signal to redirect new contributions toward the underweight asset instead of selling anything.
Understanding the inputs
Total portfolio value should cover all your investment accounts together — 401(k), IRA, and taxable brokerage. Rebalancing works across the whole portfolio, not account by account, because managing each separately forces avoidable taxable trades.
Current percentages come from your actual holdings today, and they need to sum to 100. Target percentages are the allocation you decided on, not what feels right after a good or bad year. A common starting point is 110 minus your age in stocks, with the remainder split between bonds and cash. Cash is typically 5 to 10 percent — enough for near-term needs and opportunistic buying.
How is this calculated?
Amount to Buy/Sell = (Target % − Current %) × Total Portfolio. Positive = buy, negative = sell.
A worked example
Suppose you hold $250,000 across all accounts, currently 72 percent stocks, 20 percent bonds, and 8 percent cash after a strong equity year. Your target is 60/30/10.
The calculator shows you need to sell $30,000 of stocks, buy $25,000 of bonds, and move $5,000 into cash. Now consider where. If $30,000 of your stock position sits in a 401(k), sell it there and the transaction is tax free. Sell the same $30,000 in a taxable account with a $10,000 embedded gain and you owe roughly $1,500 at the 15 percent long-term capital gains rate — enough to make redirecting contributions the better route if you are close to target anyway.
Limitations and assumptions
The calculator produces a pure arithmetic answer and ignores everything that makes rebalancing costly in practice: capital gains tax on sales, bid-ask spreads, wash sale rules if you are also harvesting losses, and any redemption fees. In a taxable account those costs can exceed the benefit of a small correction.
It also models three broad buckets only. It cannot handle allocation within equities — domestic versus international, growth versus value, large versus small — or alternatives, real estate, and crypto. Nothing here suggests a particular allocation is right for you, and rebalancing does not protect against loss. Market returns are not predictable, and this is not investment advice.
Common Questions
- Why does a portfolio need rebalancing at all?
- Because assets grow at different rates, so the mix drifts away from what you chose. A 60/40 portfolio in a year where stocks return 20 percent and bonds 2 percent ends the year at roughly 64/36. Left alone across a long bull market, a moderate portfolio quietly becomes an aggressive one.
- How often should I rebalance?
- Annually is the common default and performs about as well as anything more frequent. The main alternative is threshold rebalancing — acting only when an allocation drifts more than 5 percentage points from target. Research finds little difference between reasonable approaches; the cost of rebalancing too often usually exceeds the benefit.
- Does rebalancing improve returns?
- Not reliably. Over long periods it usually reduces returns slightly, because it trims the best performing asset. What it does is control risk, keeping your portfolio at the level of volatility you actually chose. Treat it as risk management, not a return strategy.
- How do I rebalance without triggering capital gains?
- Rebalance inside tax-advantaged accounts first — trades in a 401(k) or IRA have no tax consequence. In taxable accounts, direct new contributions and dividends toward the underweight asset instead of selling the overweight one. Selling appreciated stock in a taxable account can cost 15 or 20 percent of the gain in federal tax.
- What if I cannot bring myself to sell the winner?
- That is the normal reaction, and it is exactly why rebalancing works as a discipline. Selling what has risen and buying what has lagged feels wrong every single time. If the emotional friction is too high, use new contributions to correct the drift instead — slower, but psychologically far easier to sustain.
- Does rebalancing cost anything?
- In a taxable account, potentially quite a lot. Most major brokerages now charge zero commission on stock and ETF trades, but capital gains tax on sales is real: at a 15 percent long-term rate, selling $30,000 with a $10,000 embedded gain costs $1,500. Bid-ask spreads on thin ETFs add a little more.
- Should my target allocation change over time?
- Yes, gradually. Most people reduce equity exposure as their horizon shortens, since a portfolio you will draw on within five years has less time to recover from a fall. Target date funds automate this glide path. Just do not confuse a planned shift in target with a reaction to recent market moves.
- What counts as cash in an allocation?
- Money market funds, Treasury bills, high-yield savings, and short CDs. Most portfolios hold 5 to 10 percent, enough to fund near-term needs and to buy during a downturn without selling anything. Cash sitting above that level is usually an unmade decision rather than an allocation.
- Do I need to rebalance every account separately?
- No — look at your allocation across all accounts combined, then execute trades wherever it is cheapest, which usually means inside a 401(k) or IRA. Managing each account to the same target independently forces unnecessary taxable trades and generally leaves you worse off.
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