Asset Allocation

Asset allocation is the division of a portfolio across asset classes: stocks, bonds, cash, and alternatives such as real estate or commodities, set before any individual fund is chosen. The famous Brinson study of US pension portfolios attributed the overwhelming majority of return variation over time to the allocation rather than the fund picks, which is why the decision outranks everything that follows. In the US, the default expression is the target-date fund, which owns the allocation and shifts it automatically as retirement approaches. An 80/20 split of assets returning 9% and 5% expects 8.2% a year, which is the arithmetic underneath every model portfolio.

The allocation is a risk decision disguised as a return decision. Equities drive the long-run growth and the drawdowns; bonds cushion the falls and drag the ceiling; cash preserves principal and loses to inflation slowly. Choosing the split is choosing which of those trade-offs you live with, and it should follow from your time horizon and risk tolerance. Everything after the allocation, from fund picks to tax placement, refines a decision that is already made.

The mechanics start with the classes, because each one has a job. Equities deliver the highest long-run growth with the deepest drawdowns; bonds provide income and a cushion that usually falls less; cash preserves principal and loses to inflation slowly; alternatives such as real estate add a different return stream. The portfolio's expected return is the weighted average across the classes. Take a $750,000 portfolio split 80% stocks at 9%, 15% bonds at 5%, and 5% cash at 4%: the expectation is 8.15% a year, or roughly $61,100 in the first year.

The allocation then moves over time along a glidepath, shifting from growth toward income as the goal approaches: a target-date fund running 90/10 stocks-and-bonds at age 25 drifts toward 50/50 by 65, and the expected return falls with it because the risk falls with it. Left alone, market moves rewrite the split: a 20% stock year turns 60/40 into roughly 66/34, which is more risk than anyone chose. Rebalancing once a year, or on a 5-point band, sells the winners and restores the allocation you actually picked. The asset allocation arithmetic is simple; the discipline is not.

Asset allocation is the one investment decision most Americans make whether or not they make it on purpose: the 401(k) default fund owns one, the 60/40 in a brokerage account is one, and the account assembled fund-by-fund over years is one, assembled badly. The SEC's investor guidance and the target-date fund industry both treat the allocation as the primary decision because the evidence says it is. Getting it right once beats optimizing anything else for a decade.

I watched a colleague named Brent (yes, that Brent) build a 401(k) fund by fund over six years and end up 94% equity without ever setting a split. He made forty small decisions and never noticed they composed into one large one. The 2022 drawdown noticed for him.

The highest-leverage thing most Americans can do is set the allocation once to match their horizon, automate it in a low-fee target-date fund or a rebalanced mix, and stop re-deciding annually. Run the split through the asset allocation calculator and the drift through the portfolio rebalancing calculator.