London-NY overlap

Both books are open at once. That is the entire mechanism, and everything else follows from it. From 8am to noon Eastern, London's desks are still working (it is 13:00 to 17:00 there) and New York's have just sat down. The [BIS Triennial Survey](https://www.bis.org/statistics/rpfx25_fx.htm) for April 2025 booked about 38% of global FX turnover in the UK and about 19% in the US. So for those four hours, the two locations that between them account for roughly 57% of the world's foreign exchange are live simultaneously. That is not a mild improvement in conditions. It is the deepest order book the market produces all day. ### What depth actually buys you - Tighter spreads, because more market makers are competing to quote you. - Cleaner fills, because more resting orders sit at each level for your order to hit. - Moves with follow-through, because there is enough size on the other side to build a real position into. Cost is the underrated one. The spread is a fee you pay on every single trade you ever place, and it is at its thinnest exactly when the most participants are present. ### The trap hiding in the calendar Your session times are not fixed, because the UK and the US do not change their clocks on the same days. [NIST](https://www.nist.gov/pml/time-and-frequency-division/popular-links/daylight-saving-time-dst) states US Daylight Saving Time begins on the second Sunday of March and ends on the first Sunday of November. [GOV.UK](https://www.gov.uk/when-do-the-clocks-change) states UK clocks go forward on the last Sunday in March and back on the last Sunday in October. So for two to three weeks each spring, and again for about a week each autumn, the gap between London and New York is four hours instead of the usual five. The overlap does not sit where it sat last month. If you are leaning on a session indicator, a broker's server clock, or simply a habit formed in the other half of the year, you can turn up an hour out of position and mistake a thinning book for a quiet market. ### Keep the framing honest Highest liquidity does not mean lowest risk. It means the fastest, most crowded, most decisive hours on the clock. Cheapest to trade in is not the same thing as easiest to trade in.