Key takeaways
- Allocation is the deliberate division of a portfolio across asset classes.
- Research repeatedly finds the mix explains more of a portfolio’s behavior than individual picks.
- A written target turns the mix into a measurable policy — drift is the gap that then grows on its own.
What allocation actually is
Every portfolio, deliberate or not, has an allocation: some fraction in stocks, some in bonds, some in cash, perhaps slices elsewhere. Allocation is simply making that division on purpose — choosing percentages that match your horizon and your tolerance for watching balances swing, then maintaining them.
Why the mix dominates picking
Decades of research point the same direction: the split between asset classes explains far more of a portfolio’s behavior — its growth potential and its volatility — than which particular securities sit inside each class. That inverts the beginner instinct. The glamorous question (“which stock?”) matters less than the structural one (“how much in stocks at all?”).
The main ingredients, by behavior
Described by behavior rather than recommendation: stocks have historically offered the most long-run growth with the largest swings along the way; bonds have generally been steadier with more modest returns; cash barely moves and quietly loses purchasing power to inflation — the price of being instantly available. A mix exists because no single ingredient does every job.
Targets and drift
A written target — say 60/30/10 — turns allocation from a vibe into a policy you can measure against. Because classes grow at different speeds, the actual mix wanders from the target over time. That wandering is allocation drift, and it is measured in percentage points and dollars, not judged. Drift is not an emergency; it is the maintenance signal.
A worked example
Example · a 60/30/10 portfolio, one year later
A portfolio targeted at 60% stocks, 30% bonds, 10% cash grows unevenly for a year and now sits at $70,200 / $30,900 / $10,100 — actual weights of about 63.1%, 27.8%, and 9.1%.
Stocks are roughly $3,480 above their target share; bonds about $2,460 below; cash about $1,020 below. Whether and how to close those gaps is entirely the owner’s policy — the measurement just makes the conversation possible.
Rebalancing as maintenance
Rebalancing means steering the mix back toward target — by selling overweight classes, or more gently by directing new contributions to underweight ones. Many written policies act only when drift exceeds a band of around five points, precisely to avoid constant tinkering. The discipline’s quiet virtue: it has you systematically adding to whatever has lagged, on schedule instead of on emotion.
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