When stocks rally and bonds sit still, your carefully chosen 60/40 portfolio quietly turns into 70/30 — you now own more risk than you planned for. Rebalancing is the disciplined act of trimming what has grown and topping up what has lagged, so your risk exposure stays where your long-term policy says it should be. This calculator takes your current two-split holdings and your target percentages, then tells you exactly how many dollars to sell from one sleeve and buy of the other.
The math is deliberately simple: target dollars equal your total portfolio times your target percentage, and the trade equals the gap between what you hold today and what that target says you should hold. One positive number (sell) and one negative number (buy) move the whole portfolio back onto policy, usually in a single pair of trades.
How to Use
- Enter the Current Stocks Value — the total market value today of every stock holding in the account you want to rebalance. This includes US broad-market index funds, international funds, and any equity ETFs or individual shares.
- Enter the Current Bonds Value — everything fixed-income: bond index funds, Treasuries, CDs, money market funds, and cash earmarked for the bond side.
- Set your Target Stock Allocation as a percentage. The classic moderate policy is 60% stocks / 40% bonds; aggressive investors use 80/20, conservative ones 40/60. The bond target is filled in for you as 100 minus this number.
- Read the result card. The two highlighted lines tell you the dollar trade on each sleeve: a positive number means sell that much, a negative number means buy that much. The drift line shows how far your current split has wandered from policy.
The engine computes the total portfolio, the dollar target for each sleeve, and the rebalance trade. If both trade lines land at zero, you are already on target and no action is needed.
The Rebalancing Formula
Rebalancing is just a target-weight reconciliation. Let T be your total portfolio value, s your target stock weight in percent, and c_s / c_b your current stock and bond dollar values.
- T = c_s + c_b
- Target stocks = T × s / 100
- Target bonds = T × (100 − s) / 100
- Stock trade = c_s − Target stocks — positive means sell stocks, negative means buy stocks.
- Bond trade = c_b − Target bonds — positive means sell bonds, negative means buy bonds.
Because the two legs sum to zero (one side's sell is the other side's buy), a single pair of trades restores the policy split without adding or removing any money from the portfolio.
Worked example: a $100,000 portfolio that drifted to $70,000 stocks and $30,000 bonds against a 60% stock target. Target stocks are $60,000, so the stock trade is $70,000 − $60,000 = +$10,000 (sell). Target bonds are $40,000, so the bond trade is $30,000 − $40,000 = −$10,000 (buy). Sell $10,000 of stocks and buy $10,000 of bonds — done.
Why Rebalance At All
Left alone, a portfolio drifts toward whatever has performed best. Over a long bull market, a 60/40 starting point can drift to 75/25 or higher, quietly loading you with equity risk just as valuations stretch. Rebalancing enforces the uncomfortable rule "sell what went up, buy what went down" — which is the mechanical form of buying low and selling high. Studies from Vanguard and the Financial Analysts Journal repeatedly show that periodic rebalancing either modestly improves risk-adjusted returns or at least keeps portfolio volatility in line with your tolerance, which is the real goal.
Two common rules trigger a rebalance: calendar (annually, semi-annually, or quarterly) and threshold (rebalance only when a sleeve drifts more than ±5 percentage points, or ±25% relative to its target). The threshold approach trades less often and therefore racks up less tax and commission, which is why many Bogleheads-style investors prefer it.
Examples
Example 1 — The classic 60/40 drift. A couple holds $70,000 in a total US stock index fund and $30,000 in a total bond index fund, with a 60% target. The calculator shows a $10,000 stock sell and a $10,000 bond buy, and a 10-percentage-point drift. They place the two trades in their IRA so no capital-gains tax is triggered.
Example 2 — Already on target. A recent retiree has $60,000 in stocks and $40,000 in bonds against a 60% target. Both trade lines read $0.00 and drift is 0.0 percentage points — no action needed this quarter.
Example 3 — Underweight stocks. A saver whose bonds grew after a flight to safety holds $40,000 in stocks and $60,000 in bonds against a 60% stock target. The calculator shows −$20,000 on the stock line (buy) and +$20,000 on the bond line (sell). Selling bonds to buy stocks feels counterintuitive after a stock scare, but that is exactly what the policy demands.
Example 4 — A seven-figure portfolio. A $2,000,000 account drifted to $1,400,000 stocks and $600,000 bonds. Target stocks are $1,200,000, so the engine flags a $200,000 stock sell and a $200,000 bond buy. On a taxable account this size, sequencing the trades across the tax-year and harvesting losses first matters as much as the dollar amount.
FAQ
How often should I rebalance my portfolio?
Most investors rebalance once or twice a year, or whenever a sleeve drifts more than ±5 percentage points from its target. More frequent trading raises costs and taxes without reliably improving results; less frequent trading lets risk quietly creep up. Pick a calendar date (every birthday, every New Year) and stick to it.
Should I rebalance with new contributions instead of selling?
Yes, when you can. Directing new 401(k) contributions or monthly savings into the under-weighted sleeve avoids selling appreciated assets and the capital-gains tax that comes with it. Only sell when the gap is large enough that contributions alone cannot close it within a reasonable period.
What is the difference between calendar and threshold rebalancing?
Calendar rebalancing trades on a fixed schedule (annually, quarterly) regardless of how far the portfolio has drifted. Threshold (or "band") rebalancing trades only when a sleeve moves outside a preset band — commonly ±5 percentage points absolute, or ±25% relative to the target. Threshold rebalancing typically trades less often and is more tax-efficient.
Is rebalancing a guaranteed way to beat the market?
No. Rebalancing does not promise higher returns; it promises that your portfolio's risk stays matched to your plan. In a strong, sustained bull market it can actually lag a buy-and-hold portfolio because it trims winners. Its value is behavioral — forcing discipline and preventing you from taking more risk than you can stomach.
Do I rebalance inside my 401(k) or my taxable account first?
Tax-advantaged accounts (IRA, 401(k), 403(b)) are the cheapest places to rebalance because trades there trigger no current tax. Start there. Save taxable-account rebalancing for when the drift is large, and pair those sales with tax-loss harvesting where possible.
What is a reasonable target stock/bond split?
A common starting point is 100 minus your age in stocks (so a 40-year investor holds roughly 60% stocks, 40% bonds), adjusted up or down based on your risk tolerance and time horizon. Young investors saving for retirement decades away often use 80/20; near-retirees often shift to 50/50 or 40/60.
Disclaimer
This portfolio rebalancing calculator is provided for informational purposes only and does not constitute investment, tax, or financial advice. It models a simple two-sleeve (stocks versus bonds) rebalance and ignores transaction costs, taxes, fund minimums, automatic dividends, and every other asset class. Actual rebalancing decisions should reflect your full financial picture, time horizon, and tax situation. Consult a fiduciary financial advisor before executing trades.