The Halloween strategy, Halloween effect, or Halloween indicator is a market timing strategy based on the hypothesis that stocks perform better from Oct. 31 (Halloween) to May 1 than they do from the beginning of May through the end of October. The strategy posits that it is prudent to buy stocks in November, hold them through the winter months, then sell in April, while investing in other asset classes from May through October. Some who subscribe to this tactic say not to invest at all during the summer months.