How Trade Execution Works

At a glance

Matching rule: Price first, then time, on most exchanges
Where costs appear: Spread, routing, impact, and fees
Settlement: Typically one business day after trade for US equities
Who guarantees it: A central clearing house, for exchange-traded products

Key takeaways

Your order travels through your broker, a routing decision, and a matching engine before it becomes a trade, and each step can affect the price you get.
Most exchanges match on price first and then time, which is why being early in the queue at a given price has real value.
Routing decisions, including whether your order is sold to a wholesaler, materially affect fill quality even when commissions are zero.
Clearing houses stand between buyer and seller on exchange-traded products, which is why counterparty risk is minimal there and significant on unregulated venues.
Settlement is the legal transfer of ownership and occurs after the trade, which matters for cash accounts and for corporate action eligibility.

The path of an order

1
Submission
You send an order specifying instrument, side, quantity, and type. Your broker validates buying power, position limits, and instrument eligibility.
2
Routing
The broker decides where to send it: a public exchange, a wholesaler that pays for the flow, an internal pool, or a dark venue. This decision affects your fill quality more than most retail traders realise.
3
Matching
At the venue, the matching engine pairs your order against resting orders according to its priority rules, usually price first and then time of arrival.
4
Fill and confirmation
The trade executes, possibly in several pieces at different prices. You receive confirmations; the position is economically yours immediately.
5
Clearing
A clearing house becomes the counterparty to both sides, guaranteeing the trade and netting obligations across all participants.
6
Settlement
Ownership legally transfers and cash moves, typically one business day after the trade for US equities. Until then you hold a claim rather than the asset.

How the matching engine decides

Order book, buy side at 50.10:
   Order A: 500 shares, arrived 09:31:02.118
   Order B: 300 shares, arrived 09:31:04.507
   Order C: 900 shares, arrived 09:31:09.883

A market sell order for 600 shares arrives:
   500 fill against Order A   (best price, earliest time)
   100 fill against Order B
   Orders B (200 remaining) and C are untouched

Implications:
   - Being early in the queue at a price has real value
   - Cancelling and replacing loses queue position
   - This is why latency matters to liquidity providers
   - Some venues use pro-rata allocation instead, which
     rewards size rather than time

Price-time priority in action.

Queue position is a genuine asset for anyone providing liquidity. It is also the reason that amending an order is usually implemented as a cancel and replace, which sends you to the back of the queue, and why doing so repeatedly is costly.

Routing and where your order actually goes

Destination	What happens	Effect on you
Public exchange	Order rests or executes on a lit order book	Transparent; you may add liquidity and earn rebates
Wholesaler / internaliser	A market maker fills your order off-exchange	Often price improvement over the quote; the broker may be paid
Dark pool	Matched without displaying the order	Reduced information leakage; uncertain fill
Broker internal crossing	Matched against another client of the same broker	No exchange fee; quality varies
Smart order router	Split across venues seeking best execution	Better fills for larger orders; more complexity

Retail orders are frequently routed to wholesalers who pay brokers for the flow. The arrangement is widely debated: retail orders often receive prices slightly better than the public quote, while the broker’s incentive is not perfectly aligned with yours. See dark pools and payment for order flow.

Where the costs appear

Step	Cost incurred	How to reduce it
Order submission	Commission, where charged	Broker selection; volume tiers
Crossing the spread	Half the spread per side	Use limit orders where the strategy permits
Matching against depth	Slippage on orders larger than the top level	Split large orders; trade liquid instruments
Routing	Price improvement gained or lost	Measure fills against the midpoint at order time
Venue fees	Taker fees, or maker rebates received	Order type and venue selection
Financing	Margin interest or borrow fees	Avoid unnecessary leverage and shorts
Settlement	Currency conversion, where applicable	Hold balances in the traded currency

Clearing, settlement, and counterparty risk

On exchange-traded markets, a central clearing house interposes itself between buyer and seller, becoming the counterparty to both. This means you do not depend on the creditworthiness of whoever took the other side of your trade.

Central clearing removes bilateral counterparty risk for exchange-traded equities, futures, and listed options.
Netting reduces settlement obligations. A participant who bought and sold the same instrument settles only the difference.
Margin at the clearing house protects against member default and is why futures positions are marked to market daily.
Over-the-counter markets lack this. Spot forex with a dealing-desk broker and most crypto exchanges leave you exposed to the venue itself.
Segregation of client assets is a separate protection, determined by regulation rather than by clearing.
Settlement failure is rare but possible, and the clearing house has procedures for it that do not usually involve you.

Frequently asked questions

What does price-time priority mean?

Orders at a better price execute first, and among orders at the same price, the one that arrived earliest executes first. It rewards both competitive pricing and early submission, which is why queue position has value and why cancelling and replacing an order is costly for liquidity providers.

Why did my order fill at several different prices?

Because your order was larger than the quantity available at the best price, so it consumed successive price levels in the order book. The resulting average is worse than the quote you saw, which is slippage and is a normal consequence of order size relative to displayed depth.

What is payment for order flow?

An arrangement where a broker is paid to route customer orders to a particular wholesaler, who then executes them. Retail orders routed this way frequently receive prices slightly better than the public quote, but the broker’s incentive is not perfectly aligned with obtaining your best possible fill. Measuring your own fills against the midpoint is the practical response.

How long does settlement take?

For US equities, one business day after the trade date. Futures settle daily through mark-to-market. Spot forex conventionally settles in two business days. Crypto settles on-chain or internally at the venue, often immediately. Settlement timing affects fund availability in cash accounts and entitlement to dividends.

Who guarantees that my trade will be honoured?

On exchange-traded markets, a central clearing house becomes the counterparty to both sides, backed by member margin and a default fund. On over-the-counter markets, including most retail forex and crypto, no such guarantee exists and you are exposed to the venue or dealer directly.

Test this idea before you trade it

Describe the rules in plain language and AlgoTrader AI turns them into a structured strategy blueprint with a configurable historical backtest, cost assumptions, and exportable code.

Build a backtest

Keep reading

Referenced by

Educational use only. This guide explains how a strategy works. It is not investment advice, not a recommendation, and no result described here is a forecast. Test any approach on historical and out-of-sample data, size positions conservatively, and never risk money you cannot afford to lose.