Session overlap is the four-hour window (13:00-17:00 UTC, exclusive upper bound) when both the London and New York sessions are simultaneously open. It's the highest-liquidity window of the trading day across most asset classes:
- FX: dual book-presence in EUR/USD, GBP/USD, USD/JPY produces the tightest spreads of the day.
- US equity index futures + cash equities: NY morning + late London = peak depth.
- Crypto: less directly affected (24/7 market) but volume still spikes when both desks are staffed.
- Commodities: gold, oil, copper all see their tightest intraday spreads here.
The detector buckets trades by whether their open_time falls inside the window (UTC hour ∈ {13, 14, 15, 16}) and surfaces three patterns:
- Overlap specialist — meaningful sample in both buckets, overlap materially outperforms.
- Overlap struggler — meaningful sample in both buckets, overlap materially underperforms.
- Overlap avoidant — overlap-share is < 15 % of total trades despite the trader being active enough (≥ 15 outside-overlap trades) to prove they could be in the window if they wanted.
Card stays silent when buckets are balanced (the trader's edge is regime-agnostic — no actionable finding) or when the outside-overlap baseline is too thin to claim either pattern.
Across the analysis window: 3 trades opened in the 13:00-17:00 UTC overlap window, 28 trades opened outside. Overlap-share: 9.7 %.
The three verdicts:
- Overlap specialist. You're capturing the prime liquidity window cleanly. The volatility structure of the overlap fits your setup — likely a momentum or breakout edge that benefits from the depth and order-flow density. The fix is mostly defensive: don't let the success bleed into over-trading the window. Specialists who try to size up too aggressively are the most common path back to struggler.
- Overlap struggler. Your edge breaks down in the overlap. The likely cause: your setup is calibrated for a quieter regime (Asian session, late NY, weekend crypto) and the overlap's faster-moving prices invalidate the signals before you can act. Two clean fixes: half-size in the overlap until the gap closes, OR sit out entirely and trade the windows where your edge already works. Don't grind through.
- Overlap avoidant. You barely trade the overlap despite being active outside it. Two typical causes: workday conflict (09:00-13:00 NY / 13:00-17:00 UTC clashes with European-afternoon office hours) or unconscious habit (you opened your trading routine in a different window and never reset it). The fix is conscious: decide whether avoidance is intentional. If it's a workday conflict, fine — but make sure you've actually run the experiment of trading the overlap before assuming the edge wouldn't transfer.
The Onyx-Engine reports whichever pattern is dominant in your data; balanced behaviour (the overlap bucket tracks the outside bucket within tolerance) keeps the card silent.
Why the overlap is structurally different from other hour buckets. Hour-of-day analysis (the Hour-Buckets free-tier card) shows your win-rate per UTC hour. The session-overlap card narrows that to a market-microstructure-defined window. The 13:00-17:00 UTC band isn't 'four random hours that happen to be busy' — it's the specific window where DUAL-VENUE liquidity stacks. That's why the bucket cleanly separates from outside even when individual hours within it look similar to neighbouring hours: the order-flow regime is fundamentally different.
Limitations.
- Fixed window. The overlap is hardcoded to 13:00-17:00 UTC. In US daylight-saving winter the NY session shifts to 14:30 UTC, leaving 13:00 in late London only. The card slightly over-counts the overlap in those four winter months. Future versions may DST-adjust.
- Asset-class agnostic. A FX trader and a crypto trader both get the same overlap window. Crypto is 24/7 so the overlap matters less; the card's verdict is most actionable for FX, equity-index futures, and commodity traders.
- Avoidance threshold is fixed at 15 %. Some swing traders intentionally hold positions across the overlap rather than entering inside it; the avoidance verdict will misfire on them. Read the verdict as 'check whether your avoidance is intentional', not 'you must trade the overlap'.
Tier: Pro. Wave 5 (Market Context) — closes the wave alongside Performance × Regime (TRA-226) and News-proximity (TRA-227). Pairs with Hour-Buckets (free) which shows the per-hour distribution.
How to read the card:
1. Hero (left) — verdict word + 'you win/lose/miss the overlap'. Single-glance read. 2. Four MicroStats — win-rate overlap vs outside, avg P&L overlap vs outside. Avoidance variant shows '—' for overlap-side stats since the sample is too thin to claim numbers. 3. Hint line — the rule that addresses the dominant verdict.
Re-look frequency: monthly. Trading-window habits change slowly; daily noise is irrelevant.
Tier: Pro.