# How to adjust corporate actions for VaR

I am using variance co variance matrix for calculating the VaR. Now if the some corporate action comes in between like stock split, resulting a huge VaR number on that particular day as the volatility will drop by huge amount.

For instance, if a stock price series is $\$10, \$10.25, \$10.28, \$10.54, \$10.98, \$11.65, \$11.65$and so on for the last 1 year and suddenly the stock split comes in between and the prices drops to around$\$5$, resulting in huge volatility and thus impacting my VaR number. How to adjust this as to my VaR numbers looks in synchronization?

Thanks in advance.

• I would suggest recalculate in sense of adjusted close...as explained here Aug 1, 2016 at 17:38
• That's not what I am looking for...you have the link of adjusted closing prices which will impact my volatility as in case of splits, there will be a sudden drop in the price...thus greatly impacting my VaR.
– user18663
Aug 1, 2016 at 18:14
• If you calculate it correctly then there will be no drop in price. You basically split or the prices backwards so they correspond to the same number of shares...also when computing a covariance matrix, you need to do it with returns(log returns), not prices! The comovement you want to capture is in returns of the series Aug 1, 2016 at 18:50
• Great, hope it helped. If you could tick my answer then, that would be great :) thanks Aug 1, 2016 at 19:05
• Hah...yeah sure..!!!!
– user18663
Aug 1, 2016 at 19:06

## 1 Answer

The prices need to be recalculated for 'Adjusted Close'. You basically split or the prices backwards so they correspond to the same number of shares...also when computing a covariance matrix, you need to do it with returns (log returns), not prices!

The comovement you want to capture is in returns of the series.