Half right — and quieter is not the same as safer.
August is genuinely quieter in 13 of 19 markets, and no market of 19 shows a real directional difference. But quiet on average is not the whole story: August is also where thin liquidity turns a shock into a much larger move. In 2007, 2011, 2019 and 2024, between five and eleven markets simultaneously ran 15%+ above their normal volatility. "Trade smaller in August" survives. "August is safe" does not.
| Market | In the window | Rest | z | Movement | Samples |
|---|---|---|---|---|---|
| GBP/JPY | 49.9% | 51.0% | -1.9 | 89% of normal | 7,842 |
| GBP/USD | 49.0% | 49.9% | -1.7 | 85% of normal | 11,444 |
| NZD/USD | 49.1% | 50.0% | -1.7 | 101% of normal | 11,373 |
| EUR/USD | 49.3% | 50.1% | -1.6 | 96% of normal | 12,022 |
| USD/JPY | 49.6% | 50.5% | -1.5 | 115% of normal | 7,791 |
| GER40 (DAX) | 50.4% | 51.5% | -1.4 | 71% of normal | 4,434 |
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.