Asset Allocation

The strategy of dividing a portfolio among different asset classes — stocks, bonds, cash, real estate — based on your time horizon, risk tolerance, and financial goals, to balance growth potential against volatility.

Asset allocation is the practice of dividing an investment portfolio among different categories of assets — primarily stocks (equities), bonds (fixed income), and cash or cash equivalents — in proportions designed to match the investor's goals, time horizon, and tolerance for risk. The central insight behind asset allocation is that different asset classes behave differently under different economic conditions: stocks offer higher long-term growth but greater short-term volatility; bonds provide more stability and income but lower long-term returns; cash is stable but loses ground to inflation over time. By holding multiple asset classes that don't move perfectly in sync, investors can reduce portfolio volatility without proportionally sacrificing expected return.

The most important single variable in asset allocation for most investors is the stock-to-bond ratio. A 90/10 portfolio (90% stocks, 10% bonds) maximizes long-term growth potential but experiences sharp declines in market downturns — the 2008 financial crisis saw US stocks fall approximately 50% from peak to trough. A 60/40 portfolio (60% stocks, 40% bonds) historically falls significantly less in downturns and recovers faster, at the cost of somewhat lower long-term returns. A 30/70 portfolio provides the most stability but barely keeps pace with inflation over long periods. The right allocation depends on when you need the money (time horizon) and how you'll actually behave when your portfolio drops 30% in value — many investors who said they could tolerate risk discovered in 2008 or 2020 that they couldn't, and sold near the bottom, locking in losses.

Asset allocation changes over time — typically shifting from more aggressive (higher stock percentage) to more conservative (higher bond and cash percentage) as an investor approaches and enters retirement. The reasoning: a 30-year-old with a 35-year investment horizon has time to ride out a multi-year market downturn and recover before needing the funds. A 65-year-old who needs to start drawing from the portfolio in the next few years cannot afford a 50% portfolio decline and must hold assets that preserve capital. This systematic shift toward safety is called a 'glide path,' and it's the mechanism behind target-date funds, which automatically adjust allocation based on a target retirement year.

Within each asset class, allocation decisions include the geographic breakdown (US vs. international stocks), market-cap exposure (large vs. small cap stocks), credit quality (investment grade vs. high yield bonds), and duration (short vs. long-term bonds). These sub-allocation decisions are secondary to the primary stock/bond ratio — getting the basic ratio right matters far more than fine-tuning within asset classes. For most individual investors, a simple portfolio of a US total market index fund, an international stock index fund, and a US total bond market index fund — in proportions appropriate to their time horizon — is sufficient without further optimization.

Common Asset Allocation Rules of Thumb

  • Age in bonds: hold a percentage of bonds equal to your age — 30% bonds at 30, 60% bonds at 60. Simple, but often criticized as too conservative for today's longer life expectancy and lower bond yields.
  • 120 minus age (or 110 minus age): more aggressive versions that account for longer retirements — a 30-year-old holds 90% stocks (120 − 30). Better suited for investors with pensions, Social Security income, or high risk tolerance.
  • Target-date fund glide path: the most widely used professional approach — hold a target-date fund matching your expected retirement year and let the fund manager adjust the allocation automatically over time.
  • Risk tolerance first: regardless of rules of thumb, the best allocation is one you'll actually hold through a 40% market decline without selling. If a 90% stock portfolio would cause you to sell in panic, a 70% stock portfolio you'll hold is mathematically superior.

Rebalancing

Over time, market movements cause your portfolio to drift from its target allocation. A 70/30 stock/bond portfolio in which stocks return 20% in a year becomes approximately 73/27 without intervention — you now hold more stock risk than intended. Rebalancing means selling some of the overweight asset (in this case stocks) and buying the underweight one (bonds) to return to the target. Most financial advisors recommend rebalancing once or twice per year, or whenever any asset class drifts more than 5 percentage points from target. In tax-advantaged accounts (IRA, 401(k)), rebalancing is tax-free. In taxable accounts, selling appreciated assets triggers capital gains — directing new contributions to underweight asset classes rather than selling is often more tax-efficient for routine rebalancing.

Asset Allocation for Employees with Equity Compensation

Employees who hold significant company stock through RSUs, options, or ESPP need to account for that concentration when thinking about asset allocation. A portfolio that is 60% diversified index funds and 40% individual company stock is significantly riskier than a 60/40 stock/bond portfolio, because concentrated stock positions are correlated with your employment income — the same adverse company event that reduces your portfolio value might also cost you your job. Financial advisors generally recommend keeping any single stock position (including employer stock) below 5–10% of total investable assets. Selling vested RSUs promptly and diversifying into index funds is one of the most impactful allocation decisions an equity-compensated employee can make.

Example

A 35-year-old product manager reviews her overall financial picture: she has $180,000 in a 401(k) (80% stocks, 20% bonds), $45,000 in a Roth IRA (100% stocks), and $60,000 in a taxable brokerage account (mostly unvested RSUs in her employer's stock). She realizes her effective overall allocation is heavily weighted toward a single company stock. She decides to sell RSU shares promptly upon vesting, reinvest proceeds in a diversified three-fund index portfolio, and gradually reduce her employer stock position to below 10% of total assets. She also increases her 401(k) bond allocation slightly as she approaches 40, targeting an 85/15 stock/bond split across all accounts excluding the single-stock position.