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Interpreting Split-Adjusted Historical Stock Prices

Article Quant Q&A · Author: Quant guest
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Summary

The document discusses why historical prices from a free financial data provider may disagree across chart views, historical tables, and other sources. The example concerns stock prices around a split: a pre-split closing price may look inconsistent with later values unless the series has been adjusted to account for the split. It also notes that charts and tables may use different adjustment conventions or contain unresolved discrepancies.

The response suggests that free data providers may not fully repair historical inconsistencies, while an adjusted-close field is intended to reflect corporate actions such as splits and dividends. Adjusted values can make a price series more comparable over time, but the excerpt does not verify the provider’s data or establish that adjusted close is accurate in every case. Its main practical lesson is to check adjustment methodology and reconcile historical datasets before using them in analysis or backtests.

Key ideas

  • Stock splits can make unadjusted historical prices look discontinuous when compared with later prices.
  • Charts and historical tables may disagree because they use different adjustment methods or contain data inconsistencies.
  • Adjusted-close series are intended to account for corporate actions such as splits and dividends.
  • Historical market data should be checked for adjustment issues before it is used in analysis or backtests.

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EquitiesBacktestingStatistics
Full text
# Yahoo finance inaccurate stock data


# Yahoo finance inaccurate stock data












Why is Yahoo Finance historical stock price data inaccurate? See examples: `AAPL` - actual closing prices in 2012 when AAPL previously closed > $100/share adjusted for 7:1 split; chart & data do not agree, esp when picking different time periods, e.g. "Max" vs "5 year" vs 'Custom". Historical data is also incorrect. These closing prices are wrong:

```
Sep 21, 2012 95.12 
Sep 20, 2012  94.93 
Sep 19, 2012 95.39
```

NASDAQ

Similar inaccuracies, look at charts & historical data for peak close in March, 2000 > \$5000 when Yahoo data reflects correct closing prices but Yahoo charts never get above $3100.

Apparently discrepancies are rampant..

## Answer by Rime (score 3)

https://quant.stackexchange.com/a/15758

I think this question has been answered here before (regarding yahoo finance & historical data). Most free providers of historical data do not take the time to go back & $fix$ the data discrepancies such as the one you ran into. I believe they just collect/update data as it comes I.e. Stock splits, dividend payments. However, the Adjusted Close column should reflect the most "accurate" historical price such as the High that $AAPL$ had before the split ~ $700/share is now ~$100/share after the 7:1 split.

Shown in full with attribution under the source's licence. Licence: CC BY-SA 4.0 (Stack Exchange)

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