A-Book vs B-Book Broker
Definition
A-book brokers pass client orders through to external liquidity providers (banks, ECN networks) — the broker profits from spreads/commissions and has no conflict of interest with profitable clients. B-book brokers take the opposite side of client trades internally — the broker profits when clients lose, creating a structural conflict. Most retail brokers use a hybrid model.
In-depth: A-Book vs B-Book Broker
The A-book vs B-book distinction describes the fundamental business model of how a broker handles client orders, and it has major implications for the trader-broker relationship and potential conflicts of interest.
A-Book (STP / ECN / NDD): - Client orders are routed (typically near-instantly) to external liquidity providers — banks, prime brokers, or an ECN aggregator - Broker earns through markup on the spread, fixed commissions per lot, or both - No structural conflict with client profitability — broker makes money whether the client wins or loses - Typically associated with tighter raw spreads (0.0-0.3 pips on majors) plus commission ($3-$7/lot round-turn) - Examples: pure ECN brokers explicitly market themselves as 'no dealing desk'
B-Book (Market Maker / Dealing Desk): - Broker takes the opposite side of client trades internally — when client buys EUR/USD, broker is the seller (and vice versa) - Broker profits from client losses; loses when clients profit - Structural conflict of interest — broker has incentive to want clients to lose - Defended on grounds that most retail traders lose anyway, and market-making provides better fills than passing through to thin LP liquidity - Spreads typically wider but no separate commission; broker P&L is the spread - Examples: smaller retail brokers, some bonus-driven 'no commission' brokers
Hybrid Model (most common today): - Broker categorises clients by profitability and trading style - Unprofitable clients: B-booked (broker takes other side, profits when client loses — which is most of the time at retail) - Profitable clients: A-booked (broker passes through to LPs to avoid taking losses to profitable clients) - Categorisation is automated based on account history; some brokers re-classify clients periodically - Marketing typically emphasises the A-book / ECN side; the B-book portion is rarely disclosed publicly
Implications for traders: 1. Profitable EA traders should prefer brokers that demonstrate A-book behaviour (consistent execution quality, tight slippage, no last-look) — these brokers make money from your trading regardless of your P&L. 2. B-book brokers often have specific conditions (no scalping, no news trading, minimum hold times) designed to limit the broker's downside on profitable clients. 3. The 'free trading' or 'no commission' marketing often correlates with B-book operation — the broker recovers cost through spread or P&L. 4. Pure A-book brokers are rarer than marketing suggests; verify by checking broker P&L statements (where publicly available — required for regulated entities in some jurisdictions).
Regulatory: in some jurisdictions (FCA in UK, ASIC in Australia) regulated brokers must disclose their order-handling model in client agreements. Read the relevant disclosure documents at your broker before deciding.