# How to calculate the historic volatility for FTSE 100

#### bullboy8

##### Active member
I read a mag from SG and in one of their articles it was talking about histoical volatility using SD. The one month volatility from 5th jan 09 to 5th feb 2009 was 30.95% acording to them.

I went to try to calculate this myself, first i got closing prices form yahoo finance:

FTSE 100 Historical Share Prices | ^FTSE | GB0001383545 | Yahoo! Finance UK

and worked out the % return for each day (return from the previous closing day) and applied the SD calculation, I got 1.8% for my answer. Does anyone know where I gone wrong?

2. Does anyone where i can get volatility data like this for the FTSE 100 without working it out myself?

Thanks

#### Shakone

##### Senior member
Are you sure they don't mean the monthly volatility. As in how much it changes over an entire month. And they have been calculating it for many months, and at 5th Feb, it was 30.95%?

You can see volatility on some chart packages.

#### bullboy8

##### Active member
thanks skakone...what do you mean the "monthly votatility"? i assume you mean from start to the end of the month.

this would mean 4228 - 4579 = 351 / 4228 = 8.3%

This is what it says "during the last month eg: from 5th of jan to 5th of den 2009, in average the FTSE 100 volatility has been 30.95%"

#### Calinor

##### Active member
You calculated the percentage change from two samples. It is kinda hard to know without having both the data and the original article, and it would be easier to comment if you had your calculation.

Just wondering about how you actually calculated the volatility. Outline roughly your method, and I'm sure it can easily be fixed one way or the other.

Last edited:

#### HairyMoose

##### Junior member
Hi i'm just looking at the Yahoo Data now too.
I'm not sure how to work out this Volatility thing but I subtracted month low from month high and divided by month close. (High-Low)/Close

It's interesting how much movement there is even in the quietest of months.

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