What is Asset class?

An asset class is a broad family of investments that share similar features and tend to respond to the same forces in similar ways. The main ones are stocks (shares that give part-ownership of a company), bonds (loans to governments or companies that pay interest), cash and near-cash holdings such as Treasury bills (very short-term government loans), real estate, and commodities such as gold or oil. Some investors also treat cryptocurrencies such as Bitcoin as a separate asset class. Individual holdings within a class differ, but they are usually driven by the same underlying factors, such as company profits for stocks or interest rates for bonds.

Say you invest $10,000, with $6,000 in stocks and $4,000 in bonds. In a hypothetical year, stocks fall 20% and bonds rise 5%. The stocks are now worth $6,000 × 0.80 = $4,800, a loss of $1,200. The bonds are worth $4,000 × 1.05 = $4,200, a gain of $200. The portfolio totals $9,000, a 10% fall instead of the 20% an all-stock portfolio would have suffered. In a hypothetical good year, with stocks up 20% and bonds up 2%, the result is $7,200 + $4,080 = $11,280, a 12.8% gain. Mixing asset classes narrows the range of outcomes in both directions.

The relationship between asset classes is not fixed. Correlation, a measure of how closely two investments move together, shifts over time. The three-year US stock–bond correlation was negative in 96% of months from 2000 to 2020 but positive in 94% of months from 1966 to 1999. In 2022, US inflation reached about 9%, long-term Treasuries lost about 30% and the S&P 500 fell 23.9% from peak to low, so both classes declined together. A second common misunderstanding is that owning several funds means owning several asset classes. Five different stock funds are still one asset class. The labels can also blur: high-yield corporate bonds, for example, often behave more like stocks than like government bonds.

For a private investor, the choice of asset classes and how much to hold in each, known as asset allocation, shapes most of how a long-term portfolio behaves. Over long periods the trade-off is visible in the data: a portfolio of 60% US stocks and 40% 10-year Treasuries returned about 7.9% a year since 1872, against 9.4% for stocks alone. Since 2002, a 60/40 mix of the S&P 500 and long Treasuries had a worst fall of −28% against −51% for stocks alone. Investors weigh that trade-off between growth and the depth of declines against their time horizon and their capacity to sit through losses.

By Dr. Harry Hamann, MBA

What are the main asset classes?
The core asset classes are stocks, bonds and cash. Real estate and commodities such as gold and oil are usually added as further classes. Some investors also count cryptocurrencies like Bitcoin as a separate asset class.

Is an ETF an asset class?
No. An ETF (exchange-traded fund) is a wrapper that holds investments and trades on a stock exchange. An ETF can hold stocks, bonds, gold or other assets, so the asset class depends on what the fund owns.

Is Bitcoin an asset class?
Many investors and institutions treat cryptocurrencies as their own asset class because their price behaviour differs from stocks, bonds and commodities. Others see it as too young and volatile to classify firmly. There is no single official definition.

Why do investors hold more than one asset class?
Different asset classes often react differently to the same events, so combining them can soften the overall swings of a portfolio. The benefit depends on correlation, which changes over time, and in some years, such as 2022, stocks and bonds fell together.