New Round Lots Helped Decrease Spreads

Since the Nov. 3, 2025 Reg NMS round-lot change, roughly 250 symbols (about 3% of listings) with share prices above $250 shifted to smaller round lots, affecting 23% of S&P 500 names and 40% of the Dow and representing 27% of ADVT. The change materially tightened spreads—10-share stocks saw spreads fall 50% (61bps to 30bps), 40-share stocks fell 34% (42bps to 25bps) and affected ETP spreads fell 8% (4.3bps to 3.6bps)—while NBBO displayed lower depth (NBBO depth was calibrated to retain at least $10,000). The net effect reduced the Nasdaq-100® portfolio spread from 5.5bps to 4.5bps (~1bp or ~18% lower crossing cost), lowering execution costs for institutional and retail investors though with reduced displayed depth.

Analysis

Market structure: Smaller round lots materially compress explicit spreads (10-share names ~-50%; 40-share names ~-34%; ETPs ~-8%) and cut Nasdaq-100 basket crossing cost ~1bp (~18% improvement). Winners: passive/indexed flows, retail traders executing small-sized trades, and market-making strategies that thrive on tighter quoted spreads. Losers: block liquidity providers and execution desks that rely on NBBO depth — depth fell meaningfully, increasing market-impact for >$10k trades despite NBBO depth guardrails.

Risk assessment: Immediate (days–weeks) — spreads tightened almost instantly; short-term (1–3 months) — index rebalances and quarter-end flows will monetize lower crossing costs; long-term — regulators may iterate on odd-lot/NBBO reporting, and market-making economics could prompt liquidity withdrawal under stress. Tail risks: acute liquidity evaporation in volatility spikes, a regulatory reversal or patch to NBBO size rules, and systematic algo re-pricing creating transient intraday dislocations.

Trade implications: Implement basket/ETF execution strategies to capture lower implementation shortfall (favor Nasdaq-100 exposure); prefer small-slice VWAP/TWAP executions rather than block crosses because NBBO depth is thinner. Options: favor limited-risk verticals or calendars (30–60d) on QQQ/META to exploit cheaper entry/hedge costs while capping gamma risk; avoid running large-size directional block trades in affected names without dark pool/LEO liquidity pre-trade checks.

Contrarian angles: Consensus celebrates spread tightening but underestimates realized-cost volatility for large ticket trades — decreased displayed depth can widen realized spreads in stress. Historical parallel: tick-size pilots showed well-intended microstructure fixes can generate second-order liquidity fragmentation; watch odd-lot reporting changes and dealer quoting incentives as potential future catalysts.

Key Decisions for Investors

• Establish a 2–3% tactical overweight in QQQ and/or SOXX (total notional) over 1–3 months to capture ~1bp lower crossing cost and ~18% implementation improvement in Nasdaq-100 basket trades; scale into position via 5–10k notional slices (VWAP/TWAP) to avoid depth shock.
• Initiate 1% long positions in META and ADBE (each) sized for retail-sized executions over 1–3 months; use limit orders at inside NBBO and trim if either stock’s realized spread re-widens >10bps or price underperforms benchmark by >10%.