40 years of seasonal data. AI scored daily.
Costco (COST) has historically averaged +3.9% in Nov with a 72% win rate over 40 years of data, making Nov the best month to buy COST stock. Jul is the weakest month, averaging -1.4%. TradeWave's AI currently assigns COST a long seasonal bias with a score of 72.2 and 75.7% win probability, based on 40 years of comparable seasonal windows.
Average monthly return from 1986 to 2026. Green bars are positive months, red bars are negative. The highlighted bar is COST's historically strongest month.
Based on 40 years of data (1986 to 2026). Best month is Nov, highlighted in gold.
All 12 months, based on 40 years of historical price data.
| Month | Avg Return | Win Rate | Best Year | Worst Year |
|---|---|---|---|---|
| Jan | +2.15% | 61% | +16.5% | -15.6% |
| Feb | -0.26% | 54% | +15.1% | -69.5% |
| Mar | +1.25% | 49% | +13.4% | -12.6% |
| Apr | -0.39% | 61% | +13.8% | -33.3% |
| May | +1.36% | 58% | +21.4% | -45.4% |
| Jun | +2.48% | 56% | +16.1% | -12.1% |
| Jul (worst) | -1.37% | 52% | +16.5% | -99.8% |
| Aug | -0.29% | 52% | +18.1% | -16.4% |
| Sep | +0.00% | 42% | +11.6% | -10.8% |
| Oct | +2.63% | 58% | +27.5% | -34.4% |
| Nov (best) | +3.94% | 72% | +21.4% | -15.6% |
| Dec | +0.13% | 45% | +23.6% | -13.9% |
2026 is a midterm (year 2) year in the 4 year presidential cycle. The same monthly seasonality recomputed using only prior midterm (year 2) years (1986, 1990, 1994, 1998, 2002, 2006, 2010, 2014, 2018, 2022) often tells a very different story. Months where the cycle phase diverges most from the long-run average are where seasonal edges either compound or evaporate.
| Month | All Years Avg | Midterm (Year 2) Avg | Difference | Sample (Phase) |
|---|---|---|---|---|
| Jan | +2.15% | -2.77% | -4.92 pts | 10 yr |
| Feb | -0.26% | -3.76% | -3.50 pts | 10 yr |
| Mar | +1.25% | -0.48% | -1.73 pts | 10 yr |
| Apr | -0.39% | -2.40% | -2.01 pts | 10 yr |
| May | +1.36% | +0.88% | -0.48 pts | 10 yr |
| Jun | +2.48% | +4.30% | +1.82 pts | 10 yr |
| Jul | -1.37% | -10.37% | -9.00 pts | 10 yr |
| Aug | -0.29% | -4.20% | -3.91 pts | 10 yr |
| Sep | +0.00% | -0.39% | -0.39 pts | 10 yr |
| Oct | +2.63% | +5.07% | +2.44 pts | 10 yr |
| Nov | +3.94% | +3.95% | +0.01 pts | 10 yr |
| Dec | +0.13% | -3.27% | -3.40 pts | 10 yr |
Highlighted rows show months where midterm (year 2) years diverge by more than 3 percentage points from the long-run average. Sample sizes are small by design. Each cycle phase contains roughly one year in four of historical data.
Monthly averages show you the general direction. TradeWave goes further, scanning up to 98 years of daily price data to detect specific recurring date-range windows where COST has shown the strongest historical consistency.
TradeWave has identified 84 precise windows active for COST right now, each with specific entry and exit dates and an AI-scored probability. These aren't broad monthly trends. They're exact date ranges backed by decades of historical data.
2026 is classified as midterm (year 2) in the 4 year presidential cycle. Historically, COST has averaged -11.4% returns in this cycle phase.
AI scored patterns, entry and exit windows, historical backtests, and daily picks. Free tier available.
Compare COST's seasonal trends with similar stocks. Costco's best month is Nov (+3.9% avg). See how these related tickers compare.
Seasonal analysis, not investment advice. Past performance does not guarantee future results.
Last updated 2026-07-04