The shift towards 24×5 trading in US equities is frequently described as a simple extension of market hours. According to LSEG Data & Analytics, that framing misses the bigger picture.
The real change is the erosion of a core assumption behind how markets, systems and data function: that there is a reliable overnight pause.
As US exchanges move towards near-continuous trading, LSEG Data & Analytics argues that “overnight” is losing its traditional meaning. Markets may still pause briefly, but they no longer fully switch off. Plans such as LSE 24 suggest demand for extended access is global, reaching UK equities too. For technology, data and operations teams, this raises pressing questions about how systems behave and how reliably decisions can be made when quiet periods shrink.
LSEG Data & Analytics notes that much of the debate has centred on trading mechanics, timelines and venues, while the effect on market data and operating models has received far less scrutiny. Many legacy systems were built around familiar rhythms. End-of-day processing, maintenance windows, reconciliation runs and reference data updates all relied on a long stretch of inactivity. Firms may now need to redefine trading days, reschedule processing jobs and rethink support coverage. Often, these dependencies only surface when something fails, such as a reference update falling out of sync with a trading boundary.
For data users, the earliest signs will not be dramatic volume spikes, but changes in what is visible and when. LSEG Data & Analytics expects clearer distinctions between venue-level activity, consolidated views and authoritative sources, alongside new expectations around summary statistics, end-of-day measures and corporate events.
So why accept the added complexity? Investors and platforms increasingly operate across time zones, with Asia-based participants long relying on fragmented signals such as derivatives and off-exchange activity. Rising retail investing and better trading technology are boosting both appetite and feasibility for extended access.
Overnight sessions may stay lower in volume, but LSEG Data & Analytics stresses they are becoming high-sensitivity windows, where corporate news or geopolitical developments can give a small number of trades outsized influence. Overnight trading already exists through venues such as Blue Ocean ATS, whose data LSEG distributes. Meanwhile, peak message rates on LSEG Real-Time have nearly doubled in recent years, reaching 27 million messages per second in May 2026.
Major US exchanges have proposed expanding the 04:00 to 20:00 ET trading day to roughly 21:00 to 20:00 ET, with a one-hour maintenance break. Applications from Nasdaq, Cboe EDGX, NYSE Arca, 24X Exchange and MEMX, alongside proposed changes from both Securities Information Processors (SIPs), signal coordinated change. Yet only four, possibly five, of the eighteen US equity exchanges plan to trade overnight initially, so the transition will be phased.
LSEG Data & Analytics concludes that firms which identify where their workflows depend on quiet periods will be best placed to adapt as conventions evolve.
For more, read the full report here.
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