Why you should NOT download historical data from yahoo finance


Today I will be looking at historical data from yahoo finance, and why you should not download from yahoo.

For comparison, I went and downloaded historical data from yahoo finance for IBM. The screen shot of the data is below.
I also downloaded IBM data from the daily download page in Metastock format. The screen show of this is also shown below.

Lets take a closer look at the data.

historical stock data comparison

The image on top is historical data from yahoo finance of 'IBM'.
The image below is metastock format of 'IBM' data.

There are significant differences between the two:
- Missing stock symbol in yahoo finance's data.
- Date formats are different. Yahoo's data is dd/mm/yyyy, but metastock is yyyymmdd.
- Yahoo finance has an extra column 'Adj Close'.
- Open, high, Low, Close, and Volume are the same for both samples.

These differences come into effect if you decide to import your data into technical software programs for charting, analysis, or automated trading. Most software programs accept data in metastock format. They do not accept historical data in yahoo's format.

Users can manually modify the data themselves. i.e. download the data, insert a new column for the stock symbol, reformat the date, and remove the last unnecessary column. This only takes about 4 minutes per file. But Yahoo only allows you to download stocks one at a time. So you will have to manually make the modifications to about 2000+ files of historical data. That's about 5.5 days if you wanted to analyse one stock exchange.

Don't get me wrong, yahoo finance is a great source of historical data. But it just isn't in the right format for importing, and it is limited to one stock at a time. To bypass this limitation, I've created two download functions that will perform the manual reformatting for you. Both functions take advantage of yahoo's free data, and also automatically modifies it into metastock format as well. Best of all, its free.

I hope these historical stock data downloads will help other investors.