XAUUSD 15m: which hour does a London session set in UTC miss?GoldOANDA:XAUUSDGuilleMustafaTHE QUESTION Say a gold strategy only trades the London session, 08:00 to 16:30, and its code reads that window in UTC instead of London time. Which hours did it really cover? WHAT I MEASURED The open-source indicator "Session DST Audit: Does a Fixed-Offset Session Drift?" on this chart, with session 0800-1630, Europe/London as the reference zone and UTC as the zone under test. It counts the confirmed 15-minute bars inside either window since 1 December 2025. WHAT THE TABLE SHOWS London changed offset once in this history, on 29 March 2026 (UTC+0 to UTC+1). The two windows differed on 148 of 231 completed session days (64.1%). 7,292 bars fell in both windows, 596 in the London window only and 596 in the UTC window only. READING From late March the UTC window ran from 09:00 to 17:30 London time: it dropped 08:00 to 09:00, the first hour of the London session, and took 16:30 to 17:30 London (11:30 to 12:30 in New York) instead. On this feed the hour it dropped was the quieter one: mean volume 7,370 against 11,413 for the hour it took (0.65x), mean bar range 0.196% against 0.215%. LIMITS This Sunday, 25 October, London goes back to UTC+0, so the two windows match again until 28 March 2027. Volume is this feed's own count, and one session string on one symbol says nothing about other hours or markets. TRY IT The indicator is open source and on this chart: enter the session string, the zone it is meant for and the zone your own script or alert uses. Not financial advice.