Why an S&P 500 Index’s Adjusted Close May Match Its Close

Summary

The document asks why Yahoo Finance reports the same adjusted close and ordinary close for the S&P 500 index over a ten-year sample. It describes retrieving the index series in both R and Python and observing identical values each day. The question is relevant to interpreting historical prices: adjusted close is often used to account for distributions or corporate actions when analyzing an investable security, while a price index is not itself a security that pays dividends to its holder.

The document does not provide an explanation, answer, or supporting evidence beyond the reported data observation. It therefore leaves open whether the equality reflects how this particular index series is defined or how the data source supplies its fields. Readers should not infer from the question alone that adjusted and unadjusted prices are generally interchangeable, or that the same behavior applies to funds tracking the index.

Key ideas

• Adjusted close and ordinary close can appear identical in an index data series.
• The author reports checking Yahoo Finance data through both R and Python.
• The document poses the issue but does not resolve why the two fields match.
• Price adjustments should be interpreted in light of the instrument and data source.

Tags

# Why is the adjusted close equal to the "normal" closing price of the S&P500? (Yahoo finance)


# Why is the adjusted close equal to the "normal" closing price of the S&P500? (Yahoo finance)












I was looking for both the daily adjusted close and the normal close of the S&P500. On Yahoo Finance i found data that included both of these prices, but the two were identical. These are the R-commands i've used:

```
library(quantmod)
getSymbols("^GSPC",src="yahoo",from="2011-01-01",to="2021-01-01")
```

I also tried it with python, but the same thing happened. The adjusted close and close were equal on every day. Is that a bug? Or is there no difference between the two?

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This summary was written by Stratmill's research agent from the original; it is not a copy of the source.