Rebalancing calculator: the exact trades to get your portfolio back on target

By Tom, CPA · Updated October 25, 2026

TL;DR: Enter what you hold in US stocks, international stocks and bonds, your target percentages, and any new cash. You get the exact trades for a full rebalance, your current drift, and a new-money-only plan that directs cash to whatever is underweight so you can avoid selling.

Educational only, not tax, legal, or investment advice. Examples are illustrations, not predictions. Rules and limits change; verify current figures and talk to a qualified professional about your situation.

Rebalancing is the investing equivalent of flossing: everybody knows they should, few enjoy it, and skipping it rarely hurts until it really does. Lavish Larry "lets his winners run" until his 60/40 portfolio is quietly 85/15 right before a crash. Frugal Fran opens this calculator once a year, makes two trades, and goes back to her library book.

The math is simple but fiddly, especially across several accounts. This tool does it in one pass. Strategy background is in rebalancing strategies and the three-fund portfolio guide.

CPA Warning Label: Selling in a taxable account can realize capital gains. Run the trades inside IRAs and 401(k)s first, or use new money, before you sell anything that triggers tax.

Inputs

• Current values of your US stock, international stock and bond holdings. Add up the same asset class across every account: 401(k), IRAs, Roth, HSA and taxable.
• Target percentages for each. They must total 100%.
• New money (optional): a contribution, bonus, dividend sweep, or, for retirees, use zero and handle withdrawals separately.

If you hold more than three funds, group them. A total US fund plus an S&P 500 fund both count as US stock. A TIPS fund and a total bond fund both count as bonds, unless you track them separately on purpose.

Trades needed

The full rebalance outputs show what to buy (positive) or sell (negative) in each asset class so every class lands exactly on target, using the combined value of current holdings plus any new money.

The largest drift output is the biggest gap between any class's current weight and its target, in percentage points. Many investors use a threshold, such as 5 points, and only act when drift exceeds it. Small drifts aren't worth the trading effort or the tax.

Round the trades to whatever your funds allow. ETFs trade in shares (or fractional shares at some brokers), while mutual funds trade in dollars. Being off by a few hundred dollars doesn't matter.

The trades always net to the new money amount: sells and buys offset, plus whatever cash you added.

New-money-only mode

Selling is where taxes and second-guessing live. The new-money-only outputs show how to invest fresh cash without selling anything:

1. The tool works out each class's shortfall versus its target at the new total.
2. If your cash covers all shortfalls, it fills them and splits any remainder by your target weights.
3. If your cash doesn't cover them, it splits the cash in proportion to the shortfalls, so the most underweight class gets the most.

The final output shows the largest drift remaining after those buys. If it's still large, a partial sale may be needed. For retirees, the mirror image works: take withdrawals from whatever is overweight.

Tax note

• Trades inside traditional and Roth IRAs, 401(k)s and HSAs don't create taxable gains, so they're usually the first place to rebalance.
• In taxable accounts, selling shares held more than a year produces long-term gain. As of tax year 2026, the 0% federal rate on long-term gains applies to taxable income up to $49,450 for single filers and $98,900 for joint filers (IRS Rev. Proc. 2025-32). Low-income early retirees may rebalance in taxable accounts at little or no federal tax.
• Selling at a loss can help through tax-loss harvesting, but watch the wash sale rule if you buy substantially identical securities within 30 days before or after.
• Specific-lot identification lets you sell the highest-basis shares first; see the taxable brokerage guide.

Example

Illustration: Fran's target is 60% US, 20% international, 20% bonds. After a strong year she holds $680,000 US, $210,000 international and $190,000 bonds, $1,080,000 in total.

• Full rebalance: sell $32,000 of US stock, buy $6,000 of international, buy $26,000 of bonds. Current max drift: 2.96 points, since US is at 62.96% versus 60%.
• With $20,000 of new money and no selling: buy $5,000 international and $15,000 bonds. Max drift falls to 1.82 points.
• With $100,000 of new money: buy $28,000 of US, $26,000 of international and $46,000 of bonds, landing exactly on target at $708,000, $236,000 and $236,000.
• Typo check: if her targets added to 90% instead of 100%, the calculator stops and asks her to fix them. That's better than quietly rebalancing toward a portfolio that doesn't exist.

Because her drift is under 5 points, she might simply direct the $20,000 contribution and skip selling entirely. Next, check what the portfolio supports with the withdrawal rate calculator, and check what fees cost with the expense ratio fee calculator. If you own rentals, the rental cash flow calculator covers that side of the balance sheet.