Which months has the market historically been strongest and weakest? Average returns and win rates for SPY and QQQ across three decades.
Seasonality is the tendency for markets to perform differently depending on the calendar month, driven by fund flows, tax cycles, earnings rhythm, and plain old habit. It is a tendency, not a guarantee: the "average" hides big winners and big losers in the same month, which is why each bar also shows its win rate and its best and worst year.
The classic patterns show up clearly in the data: the "Sell in May" summer softness, the weak stretch around September (historically the worst month), and the strong Q4 run into year-end (November and December). Use it as context for position sizing and expectations, never as a standalone signal.