Payment-for-Order-Flow (PFOF)
Idea
The business model behind free trading apps: the app sells its customers' buy and sell orders to big wholesale trading firms, which execute the trades, pocket the price spread, and pay the app a rebate per share. In Q1 2021 Robinhood made $331M this way, $142M from Citadel Securities alone — concentrating roughly 40% of US retail stock orders with a single firm whose affiliated hedge fund trades on the opposite side of the same market.
The engine's definition — word for word
Business model where retail brokers (Robinhood, E*Trade, TD Ameritrade) route customer orders to wholesale market makers (primarily Citadel Securities with ~40% share, Virtu, Two Sigma Securities, Wolverine) who execute internally, capture bid-ask spread + provide small 'price improvement' to retail, and pay the broker a per-share rebate. Q1 2021 during the GME squeeze: Robinhood generated $331M in PFOF revenue, of which $142M came from Citadel Securities alone. Structural function: concentrates ~40% of US retail equity order flow under a single market-maker counterparty (Citadel Securities) whose parent entity (Citadel LLC hedge fund) operates on the opposite side of the same market. Legally firewalled; architecturally symbiotic.
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