Portfolio Rebalancing Calculator
Portfolio rebalancing means selling some of what has grown above target and buying more of what has fallen below, to maintain your intended asset allocation.
About portfolio rebalancing
Portfolio rebalancing is the act of selling assets that have grown above their target weight and buying assets that have fallen below, returning the mix to your intended allocation so risk stays constant. Without it, a 60/40 stock-bond portfolio can drift to 75/25 in a long bull market and quietly carry far more equity risk than you signed up for.
The calculator turns your target percentages and current dollar values into the exact buy and sell amounts that restore the target mix, plus the cash flow you need to deploy if you have new contributions ready. Rebalancing is a risk-management tool first and a returns tool second: it keeps your portfolio standing where you decided it should stand, regardless of what the market did this year.
How it works
Buy / sell per asset = (Target % x Total portfolio) - Current value Drift = Current % - Target % Trigger (5/25 rule) = |Drift| >= 5pp OR |Drift| >= 25% of target
- Target allocation = the long-term mix chosen for your age, goals, and risk tolerance, e.g. 60% stocks, 30% bonds, 10% cash.
- Current value = present market value of each asset class (not cost basis).
- Buy amounts sum to total sell amounts, since rebalancing only shuffles within the portfolio.
Worked example
An investor with a $500,000 portfolio targets 60% stocks / 30% bonds / 10% cash. After a strong year stocks ran to 70% of the mix while bonds and cash fell behind:
- Target dollars: Stocks $300,000, Bonds $150,000, Cash $50,000.
- Current dollars: Stocks $350,000, Bonds $110,000, Cash $40,000.
- Stock action: $350,000 - $300,000 = sell $50,000.
- Bond action: $150,000 - $110,000 = buy $40,000.
- Cash action: $50,000 - $40,000 = buy $10,000.
- Net check: -$50,000 + $40,000 + $10,000 = $0. The portfolio is rebalanced without new cash.
Rebalancing strategies compared
| Strategy | Trigger | Pros | Cons |
|---|---|---|---|
| Calendar annual | Once a year on a set date | Simple, predictable, minimal trades | Can let drift accumulate up to 11.9 months |
| Calendar quarterly | Four times a year | Catches drift sooner | More trades, more tax events in taxable accounts |
| 5/25 threshold | 5pp absolute or 25% relative drift | Trades only when drift is meaningful | Requires monthly monitoring |
| Cash flow only | Direct new contributions to underweight assets | No realized gains, low cost | Slow; insufficient in a big move |
| Target-date fund | Automatic, daily inside the fund | Zero effort, no taxes inside fund | One-size-fits-all glide path |
Common pitfalls
- Rebalancing too often. Studies (Vanguard 2010, 2019) show monthly rebalancing increases transaction costs and tax drag with no risk-adjusted return benefit over annual.
- Forgetting tax-advantaged accounts first. Selling inside a 401(k), IRA, or Roth has zero tax cost. Always check whether you can do the trade there before touching a taxable account.
- Triggering wash sales. Selling a fund in taxable at a loss and rebuying a substantially identical fund within 30 days disallows the loss. Use a similar-but-not-identical replacement (e.g. VTI for ITOT).
- Ignoring cash drag. Cash that piles up from dividends and interest can quietly become 5 to 8 percent of the portfolio. Sweep it into the underweight asset class at every rebalance.
- Selling all the gains. If you have appreciated lots, sell the highest-cost-basis lot (HIFO) first to minimize tax. Some brokers default to FIFO, which usually means paying the most tax.
- Letting bonds drift in a falling-rate regime. When rates drop, bond prices rise and the bond sleeve becomes overweight. Rebalancing locks in the gain but also reduces duration exposure right when long bonds may continue to rally. Stick to the rule rather than market-timing the cycle.
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Frequently asked questions
How often should I rebalance my portfolio?
Vanguard's 2010 research found that calendar rebalancing (annual or semi-annual) and threshold rebalancing (5 percent absolute drift) produce nearly identical risk-adjusted returns. Annual is the simplest: pick a date you will remember, ideally not in late December when tax-loss harvesting season clouds the decision. The 5/25 rule is a popular threshold variant: trigger when an asset class drifts 5 absolute percentage points or 25 percent relative to its target.
How do I rebalance without realizing capital gains?
Direct new contributions, dividends, and bond interest into whichever asset class is underweight; that defers selling for as long as cash flow can do the work. When you must sell, do it inside tax-advantaged accounts (401(k), IRA, Roth IRA, HSA, ISA, RRSP) where capital gains are not taxed. In taxable accounts, harvest losses to offset the gains and never sell a lot within 30 days of a wash-sale buy.
Does rebalancing reduce returns?
In an arithmetic sense, modestly yes: rebalancing trims winners and tops up losers, lowering the simple average return. But the geometric (compounded) return improves because volatility is lower and the volatility drag (sigma squared over 2) shrinks. Vanguard estimates the long-run rebalancing premium at 0.1 to 0.4 percent annually for a 60/40 portfolio depending on the rebalance frequency and asset correlations.
What is the 5/25 rebalancing rule?
Coined by Larry Swedroe, the 5/25 rule rebalances when any major asset class drifts 5 absolute percentage points from target (e.g. stocks at 65 percent instead of 60 percent) OR when a sub-asset drifts 25 percent relative to its target (e.g. small-cap value at 12.5 percent vs a 10 percent target). It captures meaningful drift without churning on noise.
Should I rebalance across all accounts together or per account?
Rebalance across the household-wide portfolio, not within each account. Place tax-inefficient assets (bonds, REITs, high-turnover funds) in tax-advantaged accounts and tax-efficient assets (broad index funds, individual stocks) in taxable. When stocks drift overweight, rebalance by selling stocks in the IRA or 401(k) first, where the trade is tax-free. This is called asset location and is worth roughly 0.2 to 0.5 percent annually on a typical 60/40 mix.
Sources
- Vanguard (2010, 2019) Best Practices for Portfolio Rebalancing.
- Bernstein, William J. (2002) The Four Pillars of Investing - rebalancing bonus theory.
- Swedroe, Larry (2010) - origin of the 5/25 rule.
- IRS Publication 550 - Investment Income and Expenses, wash sale rules.