When I want the monthly volatility of stock and I only have data for about one month and I do calculation like this:
Date Close Daily Returns STDEV STDEV * 24
2015-07-15 162.1
2015-07-14 164.5 0.0148056755 0.0165791585 0.0812209576
2015-07-13 165 0.0030395137
2015-07-10 160.7 -0.0260606061
2015-07-09 158 -0.0168014935
2015-07-08 154.2 -0.0240506329
2015-07-07 154.6 0.0025940337
2015-07-06 157.5 0.0187580854
2015-07-03 160.8 0.020952381
2015-07-02 161.2 0.0024875622
2015-07-01 161 -0.0012406948
2015-06-30 156.1 -0.0304347826
2015-06-29 158 0.0121716848
2015-06-26 162.5 0.0284810127
2015-06-25 162 -0.0030769231
2015-06-24 160.7 -0.0080246914
2015-06-23 162.9 0.0136901058
2015-06-22 159.4 -0.021485574
2015-06-19 156.6 -0.017565872
2015-06-16 157.8 0.0076628352
2015-06-15 156 -0.0114068441
2015-06-12 159 0.0192307692
2015-06-11 158.9 -0.0006289308
2015-06-10 159.3 0.0025173065
So I get 8.1% in monthly volatility. Is this correct calculation or do I have to have one year of data for it to be "correct"? Cheers