A nice use of Tech Trader to de-bunk (or maybe confirm depending on your risk tolerance) the myths on these.
For buying at month's end, there's a slight bias to the long side, but not enough to trade on. If you wanted to play the strategy, the approximate best times are going in 1 day before the month end and holding for 3 days. The hitrate is about 60% - more details and the raw data here if you want to also mess around with it:
https://www.pftq.com/stocks/images/2012-10-30_16-00,_SPY_MonthEnd.csv Also thought about testing out how effective "Santa Rallies" have been, just choosing Thanksgiving weekend as the ballpark starting point and optimizing on best entry + exit. It's about the same conclusion - nothing substantial enough to be trading on imo. Hitrate is 78% if you buy in 6 trading days before Thanksgiving and hold for 25 trading days. Data is here if you want to play with it:
https://www.pftq.com/stocks/images/2012-10-30_16-00,_SPY_SantaRallies.csv