COST's current 20d return reading and what that signal has historically been followed by.
This page covers Costco (COST) — its current 20d return reading and the measured historical record of what COST 20d return extremes were followed by.
How to read this. These figures are measured only on instruments currently in our coverage — a set of companies that survived. Signals that appear to have 'worked' on the downside are conditioned on these names having recovered; a company that fell and never came back would not be here to measure. Read every number below as a property of this surviving sample, not a universal rule, and never as advice.
All figures are ‘excess’ returns — measured relative to each instrument’s own historical drift, not relative to the market. This is not alpha and not a market-beating claim; it isolates the signal from the instrument’s background trend. Measured from the first day each signal appeared (not its most extreme point), so it reflects what was knowable in real time.
Measured across COST’s 20d return history from 1986 to 2026: 52 overbought episodes and 38 oversold episodes. Overbought readings were followed by -0.97% excess at 5 sessions and -0.07% by 20; oversold readings were followed by -0.13% excess at 5 sessions and +0.52% by 20.
On this signal, COST was most recently overbought on 2026-01-21 and most recently oversold on 2026-06-17.
Measured-outcome coverage runs through 2026-06-17 — the most recent episode with forward sessions scored; the current reading above is later, as of 2026-08-21.
When COST was overbought / at a high extreme
Across 52 past episodes where COST was overbought on this signal, the close 20 sessions later lagged COST’s own trailing drift by 0.07 percentage points on average (48% of episodes beat drift).
| horizon | excess vs own drift | beat-drift rate | episodes with complete horizon |
|---|---|---|---|
| 1 session | -0.69% | 31% | 52 |
| 5 sessions | -0.97% | 42% | 52 |
| 20 sessions | -0.07% | 48% | 52 |
When COST was oversold / at a low extreme
Across 38 past episodes where COST was oversold on this signal, the close 20 sessions later beat COST’s own trailing drift by 0.52 percentage points on average (55% of episodes beat drift).
| horizon | excess vs own drift | beat-drift rate | episodes with complete horizon |
|---|---|---|---|
| 1 session | +0.31% | 58% | 38 |
| 5 sessions | -0.13% | 47% | 38 |
| 20 sessions | +0.52% | 55% | 38 |
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