Execution is the moment your buy or sell order becomes an actual trade. It is the price, size and venue at which your instruction is filled, whether in one go or in parts.
People often say an order has been executed when it is filled, but the pathway to that fill matters. Routing choices, order type and market conditions shape the final price and how quickly it happens.
What happens between clicking buy and a fill
After you submit an order, your broker runs risk checks and decides how to route it. Some platforms send it to an exchange order book, some to a market maker that quotes two way prices, and some use a smart router that compares venues for the best available outcome. If you have direct market access, your order can be placed straight into an exchange’s order book within the broker’s risk limits.
Once the order reaches a venue, the matching engine searches for willing counterparties. A market order trades against the best available quotes immediately. A limit order posts to the book or trades if opposing interest is already there. When a match is found, the trade is executed and you receive a confirmation that shows price, quantity, time, and venue or counterparty.
Execution can be full or partial. If there is not enough size available at your price, a portion may fill and the remainder can either rest, route elsewhere or cancel, depending on your instructions.
Where trades execute: exchanges, market makers and dark pools
Execution venues vary by asset class and jurisdiction, but most equity and ETF trading happens on stock exchanges and alternative venues that link to them. Off exchange execution can occur with market makers or internalisers that fill your order against their own inventory. Large institutions sometimes use dark pools, which are private venues where resting orders are hidden from public view. These aim to reduce signalling and market impact for big trades, often pricing relative to quotes on lit markets.
In bonds, foreign exchange and many derivatives, execution is often over the counter. You deal bilaterally with a bank or broker dealer that streams prices or negotiates a trade. Exchange traded derivatives like equity index futures and listed options execute on regulated exchanges through their order books.
The choice of venue influences price, speed and likelihood of fill. A fast moving small cap share might favour a market maker that holds inventory. A deep index future might favour an exchange book with transparent depth. For very large blocks, hidden venues or algorithmic slicing can reduce slippage.
Order types that shape your execution
The order type is a major driver of the execution outcome:
- Market order trades immediately at the best available prices. You prioritise speed and certainty of fill over price. In a thin market this can sweep several price levels and increase slippage.
- Limit order sets a maximum buy or minimum sell price. You control the worst acceptable price but may not get filled if the market does not trade there. It can rest in the book and provide liquidity.
- Stop or stop limit triggers only when a set level is reached. The stop converts to a market or a limit order at the trigger, which affects how it executes in fast conditions.
- Time in force instructions
Time in force settings decide how long an order tries to execute. A day order expires at the session close. Immediate or cancel tries now then cancels any remainder. Fill or kill requires the whole size or nothing. Good till cancelled can persist until you revoke it or it hits a broker’s maximum allowed duration. These choices affect whether an order posts liquidity, how long it can pick up partial fills, and how exposed it is to sudden price moves.
How brokers assess best execution
Best execution means pursuing the best possible result for clients across several factors, typically price, costs, speed, likelihood of execution or settlement, size and nature of the order. The precise rules and reporting standards vary by country and can change.
Firms measure execution quality with benchmarks such as:
- Arrival price the mid price or last traded price when the order arrived. Slippage is the difference between the achieved price and this benchmark.
- Quote improvement whether the fill improved on the displayed best bid or ask. Internalisation or hidden liquidity can deliver better prices than the screen.
- VWAP or TWAP comparison against a volume or time weighted average price over the execution window, common for sliced institutional orders.
- Fill rate and speed how much of the order executed and how quickly, important for time sensitive strategies.
Costs also matter. Explicit costs include commission and venue fees. Implicit costs include the bid ask spread and market impact from your own trading. The right balance differs by strategy and order size. A small urgent trade may accept wider spreads for speed, while a large trade may use algorithms to trade patiently and reduce footprint.
Partial fills, remainders and rejections
If only part of your order can be matched at your price, the venue will execute that portion and handle the rest based on your time in force. You might see several execution reports at slightly different prices and times as the order picks up liquidity across venues.
Remainders can be cancelled automatically, continue to rest, or be re routed by a smart order router. Rejections usually stem from failed risk checks, insufficient margin, price limits that are too far from the market, or venue outages. The broker’s platform should state whether the order is working, partially filled, fully filled, or cancelled.
Execution, allocation and settlement: not the same thing
Execution is the trade itself. Allocation is how a filled block trade is split across accounts, which matters for fund managers that bunch orders. Clearing and settlement come afterwards, when obligations are matched and securities and cash exchange ownership. Retail platforms often hide that plumbing from view, but you still see trade dates and settlement dates on your statements.
Corporate actions can interact with these stages. For example, if you buy shares just before the ex dividend date and your execution completes in time, you may be on record for the payout once settlement occurs on schedule. The details depend on market rules and the instrument.
Examples: market vs limit execution in practice
Say you place a market order to buy 1,500 shares when the best ask is 100.00 and the order book shows 800 shares at 100.00 and 1,200 at 100.02. Your trade will likely execute 800 at 100.00 and 700 at 100.02, giving an average execution price of 100.0093. You filled immediately, but part of the order had to reach the next price level, which is slippage.
Now consider a limit buy at 100.00 for the same 1,500 shares. If there are 800 available at 100.00 and nothing else at that price, you get 800 filled and 700 remain resting. If more sellers appear at 100.00, the remainder may fill. If the market lifts and never trades back to 100.00, the rest will not execute. You controlled the worst price, but accepted execution risk.
For a large institutional order, a trader might choose to slice a 200,000 share buy into smaller clips over an hour, aiming to match volume and reduce footprint. The execution quality would then be judged against a VWAP or arrival price benchmark, balancing cost against the need to finish within the window.
In short, execution is not just a tick on a trade ticket. It is the outcome of venue choice, order type and market conditions, all working together to turn your intent into a real trade at a real price.