SPX vs SPY: What's the Difference?

Many investors and financial analysts use SPX and SPY interchangeably to reference or track the performance or price movements of the S&P 500 index. However, some investors understandably confuse the two symbols and don’t realize that one is an index and the other is an ETF. 

Learn the key difference between SPX and SPY, as well as what they are and how they work.

SPX vs SPY: What’s the Difference? 

SPY is the ticker symbol for an exchange-traded fund that tracks the performance of the S&P 500 index; it is traded like a stock. SPX is simply the numerical value that represents the level of the S&P 500 index and is not directly tradable. 

Here are the basics on SPX and SPY: 

What Is SPX? 

SPX refers to the S&P 500 index, which is a stock market index that measures the performance of 500 large cap publicly traded companies in the United States. The S&P 500 index is widely regarded as one of the best measures of the overall performance of the U.S. stock market. 

SPX is a numerical value that represents the level of the S&P 500 index. It is calculated by taking the weighted average of the stock prices of the 500 companies included in the index, with the weights determined by the market capitalization of each company. SPX is often used as a benchmark for the performance of large cap U.S. stocks. 

The S&P 500 index is maintained by S&P Dow Jones Indices, a division of S&P Global. It is one of the most widely followed stock market indices in the world and is used as a benchmark by investors, analysts and financial professionals. 

What Is SPY? 

The SPDR S&P 500 ETF Trust (SPY), also known as SPY, is an exchange-traded fund that tracks the performance of the S&P 500 index. The S&P 500 is a stock market index that measures the performance of 500 large cap publicly traded companies in the United States. 

SPY was introduced in 1993 and is one of the oldest and largest ETFs in the world, with $600 billion in assets under management as of Oct. 22, 2024. SPY trades on the NYSE Arca exchange and can be bought and sold like a stock through a brokerage account. 

Investing in SPY provides investors with exposure to a diversified portfolio of large cap U.S. stocks, making it a popular choice for those looking to invest in the U.S. stock market. Because it tracks the S&P 500 index, SPY is often used as a benchmark for the overall performance of the U.S. stock market.  

Technical traders may also track SPY stock charts to watch for technical patterns from past performance that provide clues about how a stock may perform in the future.  

How Do You Invest in the S&P 500? 

You can’t invest directly in the S&P 500 index, but investors can use investments, such as ETFs and index funds, that track the performance of the index. As measured by assets under management, the largest S&P 500 ETF is the SPY ETF, but its biggest competitors, the Vanguard S&P 500 ETF (VOO) and the iShares Core S&P 500 ETF (IVV), are projected to surpass SPY's AUM by 2025. The largest S&P 500 index mutual fund is the Vanguard 500 Index Fund Admiral Shares (VFIAX).

Read our related article, Vanguard Funds: VOO vs VFIAX Comparison Guide

Bottom Line on SPY vs. SPX

SPX is a symbol referring to the S&P 500 index, which consists of the largest 500 publicly traded companies, as measured by market capitalization. Investors can’t directly invest in SPX, but they can invest in ETFs or index funds that are designed to track the performance of the index. SPY is the largest exchange-traded fund that tracks the S&P 500.