order-routing-choices-and-smart-order-types — trading and execution

When you submit an order, your broker chooses where to send it for execution. This routing decision affects your fill price, execution speed, and likelihood of getting filled. Understanding routing options and advanced order types gives you more control over trade execution.

How Order Routing Works

The U.S. equity market is fragmented across multiple venues:

Exchanges: NYSE, Nasdaq, CBOE, IEX, and others
Alternative Trading Systems (ATS): Dark pools operated by brokers and independent firms
Market Makers: Firms like Citadel Securities and Virtu that provide liquidity

Your broker must route orders according to its "duty of best execution," meaning it should seek the best reasonably available price. However, the definition of "best" involves tradeoffs between price, speed, certainty of execution, and cost.

Payment for Order Flow

Many retail brokers route marketable orders to wholesale market makers who pay for the order flow (PFOF). In exchange for receiving orders, these market makers provide price improvement relative to the National Best Bid and Offer (NBBO).

A PFOF arrangement might work as follows:

NBBO for XYZ stock: $50.00 bid / $50.02 ask
You submit a market buy order for 100 shares
Market maker fills you at $50.015 (a $0.005/share price improvement)
Broker receives $0.002 per share in PFOF

Your effective cost per share is $50.015 instead of $50.02, saving $0.50 on the trade. The broker earns $0.20 in PFOF.

SEC Rule 606 requires brokers to disclose their routing practices and PFOF arrangements quarterly.

Exchange Routing Options

Some brokers offer direct routing to specific exchanges. Each venue has different characteristics:

NYSE and Nasdaq The primary listing exchanges offer deep liquidity for their listed stocks. Orders sent here interact with displayed quotes and may receive price improvement from hidden orders.

IEX (Investors Exchange) IEX uses a 350-microsecond "speed bump" designed to reduce the advantage of high-frequency traders. Some traders prefer IEX for larger orders that might otherwise be adversely selected by faster participants.

CBOE EDGX and BZX These exchanges offer competitive pricing and different fee structures. Some have "inverted" pricing that pays rebates to marketable orders rather than limit orders.

Maker-Taker Fee Structure

Most exchanges use a maker-taker model:

Makers (limit orders that add liquidity) receive rebates, typically $0.002-$0.003 per share
Takers (marketable orders that remove liquidity) pay fees, typically $0.003 per share

For 1,000 shares:

Maker rebate: $2.00-$3.00 credit
Taker fee: $3.00 charge

Active traders who frequently post limit orders may prefer routing to exchanges with higher maker rebates.

Smart Order Types

Beyond basic market and limit orders, brokers offer advanced order types that automate execution strategies.

Stop-Limit Orders

A stop-limit order combines a stop price (trigger) with a limit price (execution constraint).

Example: You own XYZ at $50 and want to limit losses. You set a stop-limit sell with stop price $45 and limit price $44.50.

If XYZ drops to $45, the order becomes a limit sell at $44.50
The order only executes at $44.50 or better
Risk: If XYZ gaps below $44.50, your order may not fill

Trailing Stop Orders

A trailing stop adjusts automatically as the price moves in your favor.

Example: You buy ABC at $100 and set a 5% trailing stop.

Initial stop price: $95
ABC rises to $120; stop adjusts to $114
ABC falls to $114; stop triggers, order becomes market sell

Trailing stops can be set as a percentage or dollar amount. A $3 trailing stop on a $100 stock starts at $97 and rises dollar-for-dollar with price increases.

Iceberg Orders

An iceberg order displays only a portion of the total order size. You might submit a 10,000-share buy order with a 500-share display quantity. The exchange shows only 500 shares; as those fill, another 500 shares appear until the entire order executes.

This prevents other participants from seeing your full order size and potentially moving the price against you.

Fill-or-Kill (FOK) and Immediate-or-Cancel (IOC)

FOK: The entire order must execute immediately at the limit price or better, or it cancels entirely. Useful when partial fills are unacceptable.

IOC: Execute whatever quantity is immediately available at the limit price or better, then cancel the remainder. Useful for capturing available liquidity without leaving a standing order.

Worked Example: Routing and Order Type Impact

Michael wants to buy 2,000 shares of DEF Corp, trading at $25.00 bid / $25.05 ask.

Option 1: Market Order, Default Routing

Michael submits a market buy for 2,000 shares. His broker routes to a market maker.

Fill price: $25.04 (including $0.01 price improvement)
Total cost: $50,080
Slippage from midpoint ($25.025): $30

Option 2: Limit Order, Direct to Exchange

Michael submits a limit buy at $25.02, routed directly to Nasdaq.

If 2,000 shares become available at $25.02 or below, he gets filled
If the ask never drops to $25.02, his order sits unfilled
If partially filled (say, 800 shares), he waits for remaining fills
Exchange maker rebate: 2,000 × $0.002 = $4.00 (if his order adds liquidity)

Option 3: Iceberg Order

Michael submits a limit buy at $25.04 with 2,000 total shares and 200-share display.

Other participants see only 200 shares bid at $25.04
As 200-share blocks fill, new 200-share blocks appear
Reduces information leakage about order size
May take longer to fill but reduces market impact

Cost Comparison

If DEF is volatile and Michael needs certainty:

Market order: Guaranteed fill, but pays the spread plus potential slippage
Immediate execution value may exceed the $30 slippage cost

If DEF is stable and Michael can wait:

Limit order at $25.02 saves $40 per 2,000 shares vs. the market order
But risks missing the trade if price rises

Algorithmic Execution

For larger orders, some brokers offer algorithmic execution strategies:

VWAP (Volume-Weighted Average Price): Executes the order throughout the day in proportion to historical volume patterns, aiming to match the day's VWAP.

TWAP (Time-Weighted Average Price): Splits the order into equal time intervals regardless of volume patterns.

Implementation Shortfall: Minimizes the difference between the decision price and the final execution price, trading off speed against market impact.

These algorithms typically require minimum order sizes (5,000+ shares) and may incur additional fees of $0.005-$0.02 per share.

Regulatory Framework

SEC Regulation NMS establishes the framework for order routing:

Order Protection Rule: Venues cannot execute trades at prices worse than the best displayed price on other venues
Access Rule: Limits fees exchanges can charge for accessing their quotes
Sub-penny Rule: Prohibits quoting in increments smaller than $0.01 for stocks above $1

FINRA Rule 5310 requires brokers to use "reasonable diligence" to obtain the best market for customer orders.

Next Steps

Review your broker's Rule 606 disclosure to understand where your orders are routed and what payment for order flow arrangements exist
Compare available direct routing options at your broker if you trade actively and want control over execution venue
Test trailing stop orders on paper trades before using them with capital to understand how price movements trigger execution
For orders over 1,000 shares, consider using limit orders or iceberg orders to reduce market impact and information leakage
Calculate the break-even time value when choosing between immediate market execution and patient limit order fills

Order Routing Choices and Smart Order Types