We cannot tell you — and that is the honest answer.
This is not folklore. Researchers found November–April beating May–October in 36 of 37 markets, with UK evidence back to 1694. Testing it properly on our data, 13 of 18 markets lean the documented way — and not one is statistically distinguishable from zero. The reason is arithmetic: year-to-year variation is so large that detecting a 4-point effect in EUR/USD would need about 41 years, and we hold 19. The Dow would need 77 years; we hold 8. A 23-year archive contains 23 observations of an annual effect. It contains 36,005 observations of "EUR/USD in June–August trading hours" — which is why this site measures hours.
| Market | In the window | Rest | z | Movement | Samples |
|---|---|---|---|---|---|
| EUR/USD | 49.6% | 50.4% | -3.3 | 92% of normal | 70,823 |
| GBP/JPY | 50.5% | 51.4% | -2.7 | 89% of normal | 49,674 |
| ETH/USD | 49.3% | 50.3% | -2.1 | 101% of normal | 24,530 |
| NAS100 | 52.8% | 51.8% | 1.9 | 96% of normal | 19,189 |
| AUD/USD | 49.7% | 50.2% | -1.9 | 100% of normal | 67,234 |
| Gold (XAU/USD) | 50.7% | 51.2% | -1.6 | 77% of normal | 70,778 |
Bouman & Jacobsen (SSRN) · Jacobsen & Zhang
Every claim here reduces to a window on the clock or the calendar, so it can simply be checked. We compare the claimed window against the rest of the week on 23 years of hourly data across 19 markets, measuring two separate things the folklore tends to conflate: direction (does the window close higher more often?) via a two-proportion z-test, and movement (is the average move bigger or smaller?). A window can be perfectly ordinary in direction and genuinely quieter in movement — saying which is the entire point.
The bar here is |z| ≥ 2, deliberately more lenient than the |z| ≥ 3 this site applies to its own numbers: when testing someone else's claim, failing to reject it even at a lenient bar is the stronger statement.