Costco Shares Plunge 2.5% on $2.09B Volume 21st in Market Activity as Technical Weakness and Bearish Options Signal Short-Term Volatility

Costco (COST) declined 2.50% on August 21, 2025, with a trading volume of $2.09 billion, ranking 21st in market activity. The stock fell below its 200-day moving average of $973.52, signaling technical weakness. Options data highlighted aggressive bearish positioning, with the 2025-08-29 970 call option dominating trading activity, reflecting heightened short-term volatility expectations.

The decline coincided with broader retail sector pressure, though Costco’s drop was less severe than peers like Walmart. Technical indicators showed the RSI at 73.51 (overbought) and a MACD histogram of 3.96, suggesting waning bullish momentum. The stock’s proximity to key support levels near $962.23 and the 30-day SMA of $960.67 could determine near-term direction, with a breakdown potentially testing the 52-week low of $867.16.

Backtest analysis of Costco’s performance after a 2% intraday decline showed a 60% 3-day recovery rate, 70% 10-day win rate, and 65% 30-day win rate. The maximum return during the test period reached 2.5% on day 15, indicating moderate short-term resilience following sharp selloffs. This suggests historical tendencies for the stock to rebound, though recovery magnitude remains limited.