Asset allocation: how stock, bond and cash mixes have behaved

Asset allocation is how you divide money among the broad kinds of investments: mainly stocks, bonds and cash. It answers the first question of building a portfolio, before any decision about which fund or which company, and it does more than any later choice to set how much a portfolio can grow and how far it can fall.

The SEC's guide to the topic puts the reason simply: the mix that works best depends largely on your time horizon and your ability to tolerate risk. This article shows what that trade-off looked like in practice, using 23 years of real data for six mixes of US stocks and bonds, explains why the mixes behaved as they did, how rebalancing keeps a mix on target, and how target-date funds automate the whole process.

The three main asset classes

Stocks are ownership shares in companies (see What is a stock? A complete beginner’s guide to shares). They have historically delivered the highest long-run returns of the three, with the largest and most frequent losses along the way.

Bonds are loans to governments and companies that pay interest and return principal at maturity. High-quality bonds usually swing far less than stocks, pay steady income and have often, though not always, held up when stocks fell. Their prices fall when interest rates rise.

Cash and cash equivalents such as savings deposits, certificates of deposit, Treasury bills and money market funds are, in the SEC's words, the safest investments but offer the lowest return of the three. The main risk is inflation: money that earns less than prices rise loses buying power.

Each asset class does a different job, which is why mixing them works. Their returns are imperfectly correlated, so combining them smooths the ride (see Diversification: why spreading your investments reduces risk).

How stock and bond mixes actually behaved

To see the trade-off with real numbers, we combined two widely held ETFs: SPY, which tracks the S&P 500 and stands in for US stocks, and AGG, which tracks the broad US investment-grade bond market. Using Finabase's monthly closes and recorded dividends, with every dividend reinvested and the mix rebalanced monthly to its target, we followed $10,000 from the end of October 2003 (AGG's first full month) to October 29, 2026, about 23 years. No taxes, fees beyond the funds' own, or trading costs are included.

"Average per year" is the compound annual growth rate. "Volatility" is the annualized standard deviation of monthly returns. "Deepest decline" is the largest fall from a peak on month-end values. Calendar years are 2004 to 2025.

What the numbers show

More stocks, more growth. Every 20 points moved from bonds to stocks added about 1.5 to 1.7 percentage points a year in this period. Compounded over 23 years, that turned into a large gap: the all-stock portfolio ended with more than five times the all-bond one.

More stocks, deeper falls. The all-stock portfolio lost about half its value from its October 2007 peak to its February 2009 low. An investor who needed the money in early 2009, or who sold in fear, locked in that loss. The 60/40 mix's worst fall was about a third, and the 40/60 mix's about a fifth.

A little of each beat all of one. The 20/80 mix fell less at its worst (−16.2%) than the all-bond portfolio (−17.1%), while earning more. Bonds' worst stretch, from July 2020 to October 2022 as interest rates rose, came largely while stocks were still rising through 2021, and the small stock slice cushioned it. (With dividends reinvested, the all-bond portfolio had still not regained its July 2020 peak by October 2026.) That is diversification at the asset-class level.

Bonds worked in 2008 but not in 2022. In 2008 the bond fund gained 7.9% while stocks lost 36.8%, which is why the conservative mixes barely fell. In 2022, rising interest rates hurt both at once: stocks lost 18.2% and bonds 13.0%. A bond allocation reduces risk on average; it is not a guaranteed hedge.

What shapes a sensible mix

There is no single correct allocation. The SEC's guide names the two main factors, and two more matter in practice:

• Time horizon. Money needed in two years can't wait out a 51% decline. In this data the all-stock portfolio needed until March 2012, more than four years after its October 2007 peak, to recover with dividends reinvested. Money for a retirement 30 years away can wait.
• Risk tolerance. Your ability and willingness to see the balance fall. The table's deepest-decline column is the practical test: would you hold on through it?
• Goals and other resources. A pension, a stable job or a large cash cushion lets some people take more market risk; irregular income or near-term needs argue for less.
• Behavior. A mix you abandon in a crash is worse than a more modest mix you keep.

Rules of thumb exist, such as subtracting your age from a number like 110 to get a stock percentage, but they are starting points for thinking, not answers. The SEC's guide notes that an all-stock portfolio for a 25-year-old saving for retirement and an all-cash one for a family saving for a house down payment can both be reasonable, because the goals differ.

Rebalancing: keeping the mix on target

Markets move a portfolio off its target. After a strong year for stocks, a 60/40 portfolio might be 65/35 and riskier than intended. Rebalancing brings it back.

The SEC's guide describes two approaches: rebalancing on a schedule, for example every six or twelve months, or whenever an asset class drifts more than a set amount from its target. The mixes in the table above were rebalanced monthly to keep the comparison clean; in practice, less frequent rebalancing produces similar results with fewer trades.

Target-date funds: allocation on autopilot

A target-date fund, also called a lifecycle fund, holds a mix of stock, bond and other funds chosen for people who need their money around a particular year, which appears in its name, such as "Retirement 2055." Far from the date it holds mostly stocks; as the date approaches it shifts toward bonds and cash. The SEC's bulletin on target-date funds calls the schedule of that shift the glide path, and it distinguishes two kinds:

• A "to" glide path stops changing at the target date.
• A "through" glide path keeps shifting for years after it, and so typically holds more in stocks at and around the target date than a "to" fund.

Points the SEC asks investors to check:

• Funds with the same date can differ a lot. Two 2040 funds can hold quite different stock percentages at every point on their glide paths.
• The target date is not a guarantee. A target-date fund can lose money, including near and after its target date.
• Fees can stack. Target-date funds are usually funds of funds, so you pay the fund's own expenses and indirectly the expenses of the funds it holds, which appear as acquired fund fees in the prospectus fee table.

Target-date funds suit people who want one holding that rebalances and de-risks for them. They fit less well if most of your savings are elsewhere, since the fund's mix doesn't know about your other holdings.

Pitfalls

Judging a mix by its best years. The all-stock row looks best in the "became" column and worst in the "deepest decline" column. Both are part of the deal.

Changing the mix after a crash. Moving to bonds after stocks have fallen 40% turns a temporary decline into a permanent one. Decide the mix before the market tests it.

Forgetting to rebalance. Years of rising stocks can quietly turn a 60/40 investor into an 80/20 investor just before a downturn.

Assuming bonds always offset stocks. As 2022 showed, rising rates can hurt both.

Holding a target-date fund alongside a separate stock-heavy portfolio without considering the combined mix.

How Finabase helps

Portfolios show your holdings' value over time and what each one weighs in an allocation view, which makes drift from a target mix visible, with reports covering cash and dividends. The Treasury page shows yields across the curve, useful context for the bond and cash side of a mix. The strategy tool lets you write rule-based allocations, such as splitting capital across branches or holding SPY only while a rule is true, and see how they would have traded over the last two years of real prices. Finabase does not manage money or recommend an allocation.

Frequently asked questions

What is a 60/40 portfolio?

A portfolio with 60% in stocks and 40% in bonds, long used as a middle-of-the-road allocation. From October 2003 to October 2026 a 60/40 mix of SPY and AGG returned about 8% a year, with a worst decline of about 32%.

How often should a portfolio be rebalanced?

Common approaches are on a calendar, such as every six or twelve months, as the SEC's guide mentions, or when an asset class drifts beyond a set band from its target. Frequent rebalancing adds trading and possibly taxes with little benefit.

Does asset allocation matter more than picking investments?

For most diversified investors, the split between stocks, bonds and cash drives most of the difference in how much a portfolio swings, far more than which particular fund holds each part. The 23-year table shows how far apart the mixes ended.

Are target-date funds a good default?

They are a convenient one-fund way to get an age-based mix that rebalances itself. Whether they fit depends on their glide path, their fees and your other holdings, which is why the SEC suggests comparing funds even with the same target year.

Summary

Asset allocation, the split among stocks, bonds and cash, sets the basic trade-off between growth and stability in a portfolio. Over 23 years from 2003 to 2026, each step toward stocks in a SPY and AGG mix added growth and deepened the worst decline, from a 17% fall and 3% a year for all bonds to a 51% fall and 11% a year for all stocks, while modest blends showed how combining assets can lower risk below either alone. Bonds cushioned stocks in 2008 but fell with them in 2022. Choosing a mix starts from time horizon and risk tolerance; keeping it means rebalancing; and target-date funds package both into one fund, with glide paths and fees worth checking.