Glossary · Investing and personal finance
Diversification
Diversification means spreading money over many different investments, so that one bad one cannot sink the whole portfolio.
Also called: diversify, diversified portfolio, don’t put all your eggs in one basket
A third in each, rebalanced every January. Stocks alone: −49%; gold alone: −62%.
Stocks 11.1%, bonds 6.1%, gold 8.6%, to Oct 2026.
In plain words
Picture a beach town with two shops. The ice-cream shop does great in sunny summers and badly in rainy ones; the umbrella shop is the opposite. Own only one and your income depends on the weather. Own half of each and you earn about the same whatever the sky does. That is diversification.
In investing it works on two levels. Within one kind of asset: own hundreds of companies instead of three, and one company going bust barely matters. Across kinds of assets: stocks, bonds, gold and cash often rise and fall at different times, so mixing them smooths the ride.
Since 1972, the deepest fall from a high of a simple mix (one third US stocks, one third 10-year Treasuries, one third gold) was −19%. For stocks alone it was −49%, and for gold alone −62%.
Example
Ice cream and umbrellas
- Sunny year: the ice-cream shop earns +30%, the umbrella shop −10%.
- Rainy year: ice cream −10%, umbrellas +30%.
- Half in each, in any year: 0.5 × 30% + 0.5 × (−10%) = +10%.
- After one sunny and one rainy year, all in ice cream: 1.3 × 0.9 = +17% in total. Half and half: 1.1 × 1.1 = +21%, with no bad year at all.
Real investments are never this perfectly opposite, but the less they move together, the more mixing them helps.
One level deeper
What matters is correlation: how closely two investments move together, from +1 (always together) to −1 (always opposite). Mixing assets whose correlation is below +1 lowers the swings of the whole more than it lowers the average return. Harry Markowitz, who worked out the math in 1952, is often quoted as calling diversification the only free lunch in finance.
Since 1972, the one-third mix returned 9.8% a year, against an average of 8.6% for its three parts on their own. Its worst calendar year was −10.1% (2022), against −39.2% for stocks (2008). Putting the mix back to thirds every January (rebalancing) means selling a little of what has risen and buying what has fallen.
Diversification has limits. It cannot remove the risk of a whole market falling: in 2008 almost every stock fell together. In a panic, assets that usually move apart can drop at the same time. And owning many funds that hold the same stocks is not diversification at all.
Stocks, bonds, gold and a mix of all three since 1972
$1 in each in January 1972. Each asset had its own bad stretches: stocks in 1973–74 and 2008, bonds in the inflation of the 1970s and in 2022, gold for two decades after 1980. The mix, a third of each reset every January, has the smoothest line.
The numbers behind the chart
| Date | Mix: a third of each, rebalanced yearly | Stocks | 10-year Treasuries | Gold |
|---|---|---|---|---|
| Jan 1972 | $1 | $1 | $1 | $1 |
| Dec 1980 | $4.14 | $1.89 | $1.3 | $11.77 |
| Dec 1990 | $9.33 | $6.95 | $4.83 | $8.24 |
| Dec 2000 | $20.26 | $35.09 | $11.18 | $5.93 |
| Dec 2010 | $47.91 | $39.47 | $19.68 | $30.39 |
| Dec 2020 | $97.16 | $143 | $30.03 | $40.62 |
| Dec 2022 | $93.35 | $156 | $24.6 | $39.29 |
| Dec 2023 | $104 | $190 | $24.73 | $44.29 |
| Dec 2024 | $126 | $247 | $25 | $57.88 |
| Dec 2025 | $161 | $285 | $26.62 | $94.19 |
| Oct 2026 | $165 | $324 | $25.32 | $89.73 |
Why it matters
It is the simplest protection against the one mistake that can wipe you out: betting everything on one company, one country or one idea.
It makes the ride smoother, which makes it easier to stay invested when markets fall.
Cheap index funds and ETFs made it possible to own thousands of companies with a single purchase.
A common mistake
Myth: I am diversified: I own ten different tech stocks.
In fact: Ten companies in one industry tend to rise and fall together. Diversification needs investments that behave differently: other industries, other countries, other kinds of assets.
Questions people ask
How many stocks do you need to be diversified?
Classic studies found that most of the risk of single companies disappears with a few dozen stocks from different industries; an index fund owns hundreds or thousands at once. No number of stocks removes the risk of the whole market falling.
Does diversification lower returns?
It gives up the chance of having everything in the single best performer, in exchange for avoiding the worst. Since 1972, the stocks–bonds–gold mix returned 9.8% a year with a deepest fall of −19%, against 11.1% and −49% for stocks alone.
What is the difference between diversification and asset allocation?
Asset allocation decides how much goes into each kind of asset, say 60% stocks and 40% bonds. Diversification spreads the money within and across them, so that no single holding can do serious damage.
Read more on BigCapital
About the numbers
- The numbers on this page are recalculated from the data every night; the sources are listed at the end of the page.
- Gold: World Bank Commodity Price Data (The Pink Sheet), CMO-Historical-Data-Monthly.xlsx, sheet "Monthly Prices", column "Gold"; edition updated 2026-11-03; values through 2025-12 from the January 2026 edition (https://thedocs.worldbank.org/en/doc/18675f1d1639c7a34d463f59263ba0a2-0050012025/related/CMO-Historical-Data-Monthly.xlsx).
- US 10-year Treasury bonds, total return index: Robert J. Shiller, Online Data (shillerdata.com), ie_data.xls, sheet "Data": "Long Interest Rate GS10", checked against "Monthly Total Bond Returns" and "Real Total Bond Returns".
- S&P Composite price and total return since 1871, and US consumer prices: Robert J. Shiller, Online Data (shillerdata.com); total return with dividends reinvested monthly, calculated by BigCapital.
- This page explains a term. It is not investment advice.