The Correlation Between Stock and Bond Prices

When the stock market falls sharply, you may hear in the news that bond prices have actually risen. Stocks and bonds are both financial assets that people invest in, so why do their prices sometimes move in opposite directions? To understand this relationship, we first need to look at the difference between stocks and bonds. A stock represents partial ownership of a company. When investors purchase shares, they become shareholders of that company. If investors expect the company to grow and earn higher profits, demand for its stock may increase, pushing its price higher. On the other hand, if the company's future becomes uncertain, its stock price may fall. Bonds work differently. A bond is a financial instrument that a government or company issues to borrow money from investors. For example, imagine a government issues a one-year bond with a face value of $1,000 and an annual interest rate of 3%. When an investor buys the bond, they are effectively lending money to the government. If the government fulfills its obligations, the investor receives the original $1,000 plus $30 in interest after one year. But why would the price of a bond change? The reason is that investors do not have to hold bonds until they mature. They can also sell them to other investors before maturity. When this happens, the bond's market price depends partly on the terms offered by other bonds. Suppose you own a bond that pays 3% annual interest, but market interest rates rise and newly issued bonds with similar characteristics now pay 5%. Investors would naturally prefer the new bonds because they offer more interest for the same amount of money. As a result, the price of your existing 3% bond would generally have to fall to attract buyers. Now imagine the opposite situation. Market interest rates fall, and newly issued bonds offer only 1% annual interest. Your existing bond, which still pays 3%, suddenly becomes more attractive. As more investors want to buy it, its market price may rise. This illustrates an important principle: all else being equal, bond prices and market interest rates generally move in opposite directions. When interest rates rise, the prices of existing bonds tend to fall. When interest rates fall, their prices tend to rise. As a bond's price rises, its yield, which reflects the return available to someone buying it at the current price, decreases. When its price falls, its yield increases. Now that we understand how bond prices work, let's examine their relationship with stock prices. One of the most important factors affecting both assets is the condition of the economy. When the economy weakens and companies are expected to earn lower profits, investors may view stocks as increasingly risky. Concerns about the future can lead more people to sell their shares, causing stock prices to decline. But where does the money from those stock sales go? Some investors move their money into government bonds, which are often considered relatively safe investments. Government bonds are issued by national governments, and bonds issued by countries with strong creditworthiness are generally considered more likely to repay principal and interest than many corporate stocks are to preserve investors' capital. When money flows out of stocks and into government bonds, demand for those bonds may increase. As a result, stock prices can fall while government bond prices rise. This happens when investors become less willing to take risks and begin favoring assets they consider safer. Expectations of lower interest rates can also push government bond prices higher during an economic slowdown. When investors believe the central bank may cut interest rates to support the economy, market yields may decline, increasing the value of existing bonds. What happens when the economy begins to recover? Investors may become more optimistic about companies' sales and profits, increasing demand for stocks. If investors shift away from safer bonds in search of higher potential returns, stock prices may rise while government bond prices fall. For these reasons, stocks and government bonds sometimes move in opposite directions. However, this relationship does not always hold. One important situation in which both assets can move in the same direction is a period of rapidly rising inflation. Inflation occurs when prices across the economy increase over time. If inflation becomes too high, a central bank may raise its policy interest rate to help bring it under control. When interest rates rise, newly issued bonds generally offer higher yields, making existing bonds less attractive and pushing their prices lower. At the same time, companies may face higher borrowing costs. Consumers may also reduce their spending as loans become more expensive. These changes can weaken expectations for future corporate profits, putting downward pressure on stock prices. This happened in the United States in 2022. As the Federal Reserve raised interest rates rapidly to fight high inflation, both stocks and U.S. Treasury bonds experienced falling prices. Two assets that investors often expected to move in different directions suffered losses at the same time. The opposite can also happen. When inflation eases and market interest rates decline, stock and bond prices may rise together. Lower interest rates increase the relative attractiveness of existing bonds while potentially reducing borrowing costs for businesses and improving expectations for future profits. Therefore, it would be a mistake to assume that whenever stocks rise, bonds must fall, or vice versa. Depending on economic growth, inflation, interest rates, and investors' willingness to take risks, the two assets may move together or in opposite directions. The concept used to describe this relationship is called correlation. Correlation measures how closely two things tend to move together. When examining stocks and bonds, investors generally calculate correlation using their returns, or percentage price changes, over a given period rather than comparing their prices directly. If stock returns tend to be high when bond returns are also high, the two assets have a positive correlation. If stock returns tend to be high when bond returns are low, they have a negative correlation. If there is no clear pattern in their movements, their correlation may be weak. Correlation is usually expressed as a number between -1 and +1. A value closer to +1 indicates a stronger tendency for the two assets' returns to move in the same direction. A value closer to -1 indicates a stronger tendency to move in opposite directions. A value near 0 means there is little consistent linear relationship between their returns. However, just because stocks and bonds moved in opposite directions in the past does not mean they will always do so in the future. Their correlation can change as economic conditions change. It is also important to remember that not all bonds behave the same way. Government bonds issued by countries with strong creditworthiness carry different risks from bonds issued by financially troubled companies. During an economic crisis, the prices of safer government bonds may rise while corporate bonds with increasing default risk fall alongside stocks. In addition, bonds with longer remaining maturities are generally more sensitive to changes in market interest rates. So why do investors pay attention to the correlation between stocks and bonds? One of the main reasons is diversification, or spreading investment risk across different assets. For example, if an investor puts all their money into stocks, a major stock market decline could significantly reduce the value of their entire portfolio. However, if some of that money is invested in government bonds, rising bond prices during a stock market downturn may help offset part of those losses. Of course, owning both stocks and bonds does not guarantee protection from losses. As we have seen, both assets can decline when interest rates rise sharply. Diversification does not mean eliminating risk completely. Instead, it means reducing dependence on the performance of any single type of investment. Ultimately, the relationship between stock and bond prices changes as economic conditions and investor expectations evolve. When concerns about the economy grow, stocks and government bonds may move in opposite directions. When inflation and interest rates become the dominant forces in financial markets, both assets may move in the same direction. Understanding the correlation between stocks and bonds is not simply about predicting which asset will rise or fall. It is about learning how economic changes affect different financial investments and developing a broader understanding of the risks involved in investing.