On the stock page in yahoo finance, there is specified a beta value for the stock. Now is there a way to know what time period was used to calculate the beta? Is it the trailing 12 months? Does yahoo finance give a way to find beta's for customised time periods?
Citing the Yahoo Finance Help page,
Beta: The Beta used is Beta of Equity. Beta is the monthly price change of a particular company relative to the monthly price change of the S&P500. The time period for Beta is 3 years (36 months) when available.
Regarding customised time periods, I do not think so.