Last updated: July 2026
This article is for informational and educational purposes only and is not investment advice. See our full Disclaimer for details.
Our Why Young Investors Can Afford More Risk and Best ETF Portfolio for Retirement guides both apply asset allocation concepts without formally defining the term. This article covers that foundation directly — what asset allocation actually means, a famous (and widely misunderstood) piece of research about how much it matters, and the mechanics of rebalancing a portfolio over time.
The Basic Definition
Asset allocation is the strategy of dividing an investment portfolio among different asset categories — most commonly stocks, bonds, and cash, sometimes alongside alternatives like real estate or commodities — based on your goals, time horizon, and risk tolerance. It’s a decision made at the category level, separate from which specific stocks, bonds, or funds you choose within each category.
This distinction matters conceptually: choosing “70% stocks, 30% bonds” is an asset allocation decision. Choosing VTI specifically, rather than a different total-market fund, to fill that 70% stock allocation is a separate decision about fund selection within an already-chosen asset allocation.
Strategic vs. Tactical Asset Allocation
Strategic asset allocation refers to a long-term target mix — say, 70% stocks and 30% bonds — that you set based on your overall goals and generally maintain over time, adjusting only gradually as your circumstances change (such as the age-based glide path covered in our Why Young Investors Can Afford More Risk guide).
Tactical asset allocation refers to shorter-term, deliberate deviations from your strategic target — temporarily overweighting or underweighting a specific asset class based on a current market view, with the intention of eventually returning to (or adjusting) the long-term strategic mix. Tactical shifts are inherently a form of market timing, which — as covered throughout this site, including our What Is a Bull Market vs. a Bear Market? guide’s discussion of how hard bear-market timing is to execute well — is difficult to do successfully and consistently, even for professional investors.
Most mainstream guidance for individual investors leans toward setting a well-considered strategic allocation and maintaining it with periodic rebalancing, rather than actively shifting allocations tactically based on short-term market predictions.
A Famous, Widely Misunderstood Study
You may encounter a frequently repeated claim in financial media and advisor presentations: that asset allocation explains “90%” (or sometimes cited as 93.6%) of a portfolio’s returns, far outweighing the importance of individual security selection or market timing. This claim traces back to a landmark 1986 study, “Determinants of Portfolio Performance,” by Gary Brinson, Randolph Hood, and Gilbert Beebower, which examined the returns of large U.S. pension funds.
It’s worth being precise about what that research actually found, since the popularized version of the claim is commonly cited in a way that goes beyond what the original study demonstrated. The Brinson study specifically measured how much of the variability of a single portfolio’s returns over time was explained by its asset allocation policy — not how much of the difference in returns between different investors’ portfolios was explained by their different allocation choices. Subsequent research, including a well-known 2000 paper by Ibbotson and Kaplan, has argued the original finding is frequently misapplied to a broader claim it wasn’t actually designed to support, and some financial writers have directly challenged the popularized 90% figure as a distortion of the original research’s actual scope.
What survives this more careful scrutiny, and is less controversial: asset allocation is a genuinely major driver of a portfolio’s overall risk and return characteristics, and it’s a decision made deliberately in advance — unlike security selection or market timing, which depend on ongoing, harder-to-repeat skill. The exact percentage popularly attributed to this effect is less well-supported by the original research than commonly presented, but the underlying practical importance of thoughtful asset allocation isn’t seriously disputed.
The Core Asset Classes and Their General Roles
Equities (stocks) — Generally included for long-term growth potential, with correspondingly higher volatility, as covered throughout this site’s stock ETF guides.
Fixed income (bonds) — Generally included to reduce overall portfolio volatility and provide more predictable income, as covered in our What Are Bonds? guide.
Cash and cash equivalents — Generally held for near-term liquidity needs and stability, though holding too much for too long carries its own risk, as covered in our What Is Inflation? guide’s discussion of purchasing power erosion.
Alternative assets — A broader category that can include real estate (REITs, covered in our Best REIT ETFs guide), commodities like gold (covered in our Gold ETFs Explained guide), or other asset types offering different return and correlation characteristics than traditional stocks and bonds.
The Theory Behind Combining Asset Classes: Diversification and Correlation
The mathematical case for asset allocation rests heavily on the correlation concept covered in our What Is Diversification? guide: asset classes that don’t move in perfect lockstep with each other can be combined to produce a smoother overall portfolio return than any single asset class would provide alone, even without necessarily sacrificing much expected return. This general framework — combining assets with different risk/return characteristics and imperfect correlation to build more efficient portfolios — traces back to modern portfolio theory, pioneered by economist Harry Markowitz in the 1950s, which remains foundational to how asset allocation is taught and practiced today.
Rebalancing: Maintaining Your Target Allocation Over Time
Because different asset classes grow at different rates, a portfolio’s actual allocation naturally drifts away from its original target over time, even without any new contributions or withdrawals. A portfolio that started at 70% stocks and 30% bonds could drift to 80% stocks and 20% bonds after a strong multi-year stock rally, simply because the stock portion grew faster than the bond portion — not because anyone made an active decision to take on more risk.
Rebalancing is the process of periodically buying and selling holdings to bring a portfolio back to its target allocation. Two common approaches:
Calendar-based rebalancing — Rebalancing on a fixed schedule (for example, once a year or once a quarter), regardless of how far the portfolio has drifted from its target by that point.
Threshold-based rebalancing — Rebalancing whenever an asset class drifts beyond a specific tolerance band (for example, if the stock allocation moves more than 5 percentage points away from its target), regardless of how much time has passed.
Rebalancing serves a specific, somewhat counterintuitive function: it systematically involves selling some of whatever has recently performed best (since that portion has grown to be an outsized share of the portfolio) and buying more of whatever has recently underperformed — a disciplined, mechanical version of “buy low, sell high” that doesn’t depend on predicting which asset class will perform best next.
Sample Allocations by Financial Goal (For Illustration Only)
Asset allocation isn’t only about age — it’s fundamentally about matching your portfolio’s risk and time horizon to the specific goal the money is intended for. The following illustrates how allocation might reasonably differ across different goals, not a personalized recommendation:
| Goal | Time Horizon | Illustrative Allocation |
|---|---|---|
| Emergency fund | Immediate access needed | Cash/cash equivalents, minimal market risk |
| House down payment | 2-5 years | Primarily cash and short-term bonds, limited equity exposure |
| Mid-term goal (e.g., a future large purchase) | 5-10 years | A blend of bonds and equities, more conservative than a long-term retirement allocation |
| Long-term retirement savings (decades away) | 20-40+ years | Predominantly equities, gradually shifting more conservative as the goal approaches, following the glide-path logic covered in our Why Young Investors Can Afford More Risk guide |
The core principle connecting all four rows: the shorter and more fixed your time horizon, the less market volatility your portfolio can reasonably absorb without risking a shortfall right when the money is needed — a theme covered in more depth, including the concept of sequence-of-returns risk, throughout our retirement-focused guides.
Frequently Asked Questions
Does asset allocation really explain 90% of my investment returns? This is a commonly repeated claim that oversimplifies the underlying research. The original 1986 study specifically measured how much of a single portfolio’s return variability over time was explained by its allocation policy, not how much differences between different investors’ overall returns are explained by their allocation choices — subsequent research has argued the popularized figure is frequently misapplied beyond its original scope. That said, asset allocation remains widely regarded as a genuinely major factor in a portfolio’s risk and return characteristics, even without the specific 90% figure being fully supported.
How often should I rebalance my portfolio? There’s no single correct frequency — common approaches include rebalancing on a fixed annual or semiannual schedule, or rebalancing whenever an asset class drifts beyond a specific percentage threshold from its target. Rebalancing too frequently can add unnecessary transaction costs and, in a taxable account, potentially trigger avoidable capital gains taxes; rebalancing too infrequently can allow a portfolio’s risk level to drift meaningfully from its intended target.
Is asset allocation the same as diversification? They’re related but distinct concepts. Diversification, covered in our What Is Diversification? guide, refers broadly to spreading risk across many holdings. Asset allocation specifically refers to the strategic division of a portfolio among broad asset categories (stocks, bonds, cash, and others) — a particular, high-level form of diversification, though diversification also applies within each individual asset category (for example, diversifying across many individual stocks within the equity portion).
Should my asset allocation be the same across all my accounts? Not necessarily — some investors intentionally place different types of holdings in different accounts based on tax treatment, a concept called asset location, covered in our Best ETFs for a Roth IRA and Best ETFs for a Taxable Brokerage Account guides. Your overall asset allocation across all accounts combined is generally what matters most for risk management, even if individual accounts look different from each other.
Does tactical asset allocation (actively shifting allocations based on market views) work? This is a genuinely debated question in investing research and practice. Successfully and consistently timing tactical shifts requires correctly predicting market movements in advance, which has proven difficult even for professional investors to do reliably over long periods — a challenge covered in more depth in our What Is a Bull Market vs. a Bear Market? guide’s discussion of how difficult bear-market timing has historically been.
What’s the simplest way to implement a specific asset allocation? Target-date funds automate a specific age-based allocation glide path in a single fund, as covered in our Why Young Investors Can Afford More Risk guide. Alternatively, many investors build their own allocation using a small number of broad ETFs — for example, a total U.S. stock fund, an international fund, and a bond fund, each set at a chosen target percentage — and rebalance periodically using the methods described above.
This article is provided for general informational and educational purposes only and is not a recommendation to buy or sell any security. Historical research findings referenced above reflect academic studies conducted over specific historical periods and may not generalize to all portfolios or time periods. Always do your own research and consult a licensed financial advisor before making asset allocation decisions specific to your situation. Read our full Disclaimer and Privacy Policy for more information.