The decision that drives most of your portfolio's behavior
Asset allocation = the high-level decision of how much to put in each asset class (stocks, bonds, cash, alternatives). It's the most important investment decision most retail investors make. Studies suggest 80%+ of long-term portfolio performance variance comes from asset allocation, not security selection.
Why? Because asset classes have different risk-return profiles, and your mix determines your portfolio's overall trajectory. Picking the right individual stocks within an allocation matters less than getting the allocation roughly right.
The simplest framework — age-based allocation
Classic rule of thumb: hold (100 − your age) percent in stocks, the rest in bonds. So:
- Age 25: 75% stocks, 25% bonds
- Age 50: 50% stocks, 50% bonds
- Age 75: 25% stocks, 75% bonds
The logic: younger investors have longer horizons and can ride out volatility. Older investors are closer to needing the money and want stability. The rule isn't perfect (it ignores wealth, risk tolerance, other income, etc.) but it's a reasonable starting point.
Modern variants extend the stock allocation later (110 or 120 minus age) given longer life expectancies and lower bond yields. Target-date funds automate this kind of "glide path" — gradually shifting from stocks to bonds as the target date approaches.
Beyond age — the variables that actually matter
Real allocation depends on more than age:
Time horizon. Money you need in 1 year shouldn't be in stocks (too volatile). Money you need in 30 years should be heavily in stocks (compounding). The horizon doesn't depend on your age directly — it depends on when you'll need the money.
Risk tolerance. Some investors lose sleep over 10% drops; others ride out 50% drops without anxiety. Self-knowledge here matters. Better to be slightly under-allocated to stocks than to panic-sell during a crash.
Other wealth and income. A doctor with a stable high salary can take more equity risk than a freelancer with volatile income. A homeowner with significant home equity already has real estate exposure.
Goals. Saving for a house in 5 years vs. retirement in 30 years vs. legacy giving in 50 years all imply different allocations.
Tax situation. Tax-deferred accounts (401(k), IRA) vs. taxable accounts vs. tax-free (Roth) imply different optimal asset placements.
A reasonable default for most retail investors
For someone with a 20+ year horizon, no major short-term needs, average risk tolerance:
- 60-80% stocks (mix of US, international, possibly small-cap tilt)
- 15-30% bonds (mostly investment grade, some inflation-protected)
- 5-10% cash for short-term needs and rebalancing reserve
- 0-10% alternatives if you understand them
Specific exact numbers don't matter that much. The principle — heavy in stocks for long horizons, with bonds for diversification and stability — captures most of what good allocation does.
Rebalancing — keeping the allocation on target
Stocks and bonds don't move together. Over time, your actual allocation drifts from your target — stocks usually grow faster, so they take a bigger share. Rebalancing means selling some of what's grown and buying what hasn't, to return to your target allocation.
Frequency: quarterly to annually is fine. Trigger-based (when a class drifts more than 5% from target) is also reasonable. Over-rebalancing creates transaction costs and tax drag without much benefit.
Rebalancing is also a discipline tool — it forces you to "buy low, sell high" without thinking about it. Counterintuitively, that's often easier than trying to time the market discretionarily.
The takeaway
Asset allocation = how much in stocks, bonds, cash, alternatives. Drives 80%+ of portfolio variance. Depends on time horizon, risk tolerance, wealth, goals, and tax situation. For long-horizon retail investors with average risk tolerance, 60-80% stocks is a reasonable default. Rebalance occasionally to maintain target. The whole framework synthesizes everything from this track and the others — diversification (Track 3), market portfolio (lesson 9-2), CAPM thinking (9-3), passive default (9-6), and EMH-aware practical decisions (9-7).