Asset Allocation
How splitting money between stocks, bonds, and cash shapes both the growth and the bumps of a portfolio, explored with US returns from 1928 to 2025.
The short version
Asset allocation is how you divide a portfolio between broad categories such as stocks, bonds, and cash. It does more than any single pick to decide how much a portfolio can grow and how far it can fall. In US data from 1928 to 2025, an all-stock mix grew fastest but lost almost 44% in its worst year. Adding bonds gave up some growth in exchange for smaller losses. No mix is best in general; the right one depends on the job the money has to do.
By the end of this lesson, you'll be able to
- Define asset allocation and the three main asset classes
- Describe how adding bonds and cash changed growth and losses in historical US data
- Explain why the right allocation depends on the goal, not on which asset did best recently
Why this matters
Before you choose any particular fund or company, you face a bigger decision: how much of your money goes into stocks, how much into bonds, and how much stays in cash. The SEC's guide notes that some financial experts consider this the most important investing decision you'll make, even more important than the individual investments you buy.1 This lesson shows why, using real numbers.
The three main ingredients
Asset allocation. How a portfolio is divided among asset classes, such as stocks, bonds, and cash. More on this term means dividing a portfolio among different Asset class. A broad category of investments that tend to behave in similar ways, such as stocks, bonds, or cash. Glossary, broad categories of investments that behave differently. The three main ones are:1
- Stocks, which have historically had the highest returns and the biggest swings.
- Bonds, which are generally less volatile than stocks but offer more modest returns.
- Cash and cash equivalents, such as savings deposits and Treasury bills, which are the safest but earn the least, and can lose ground to inflation.
Other asset classes exist, such as real estate and commodities, and Part 2 covered them briefly. Stocks, bonds, and cash are the core of most portfolios.
What different mixes did, 1928 to 2025
The table below uses yearly returns for the S&P 500 including dividends, 10-year US Treasury bonds, and 3-month Treasury bills, compiled by Aswath Damodaran of NYU's Stern School of Business.2 Each mix is rebalanced back to its target at the start of every year. Fees, taxes, and inflation are left out, so real-world results would have been lower.
| Mix | Average yearly growth | Worst year | Losing years |
|---|---|---|---|
| All stocks | 10.0% | −43.8% (1931) | 26 of 98 |
| 80% stocks, 20% bonds | 9.3% | −35.6% (1931) | 25 of 98 |
| 60% stocks, 40% bonds | 8.3% | −27.3% (1931) | 21 of 98 |
| 40% stocks, 60% bonds | 7.2% | −19.1% (1931) | 20 of 98 |
| All bonds | 4.5% | −17.8% (2022) | 20 of 98 |
| All cash (Treasury bills) | 3.4% | 0.0% (2014) | 0 of 98 |
"Average yearly growth" is the compound rate: the steady yearly return that would have produced the same ending value. Calculated from Damodaran's data. Past returns don't predict future ones.
Three patterns stand out. More stocks meant more growth: the difference between 10.0% and 8.3% a year compounds into a very large gap over decades. More stocks also meant deeper losses: an all-stock portfolio lost about 44% in 1931 alone. And bonds weren't always a cushion: in 2022, both stocks and bonds fell sharply in the same year, which is why the all-bond mix's worst year is recent.
The rest of this lesson is for members
Still to come in this lesson: Try it, Choosing a mix is about the goal, the key takeaways, and 2 quiz questions with explanations.
Membership opens every lesson in the curriculum, the capstone projects, the interactive tools, and the members-only channels in the Hyperion Entities Discord. The first lesson of every module stays free.
Go deeper
- DiversificationPart 5: Building a Portfolio
- Modern Portfolio Theory and the Efficient FrontierPortfolio Theory and Risk (depth track)
- Target-Date FundsPart 2: What You Can Own
Notes and sources
- Investor.gov, U.S. Securities and Exchange Commission. Beginners' Guide to Asset Allocation, Diversification, and Rebalancing. Checked 2026-09-26. Back to text
- Aswath Damodaran, NYU Stern School of Business. Historical Returns on Stocks, Bonds and Bills, with annual data through 2025 (updated January 2026). Checked 2026-10-12. Back to text