Fill in forex trading: order execution explained
By Ken Chigbo, Founder, KenMacro. Published 2026-05-13.
Quick answer
A fill is the execution of a trading order, either in part or in full, at a specific price. When a broker matches your buy or sell instruction with available liquidity, the resulting transaction is the fill. The price and size of the fill determine your actual entry, which may differ from the requested level.
What is fill?
A fill refers to the completion of a trading order at an executable price. In forex, when a retail trader submits a market or limit order, the broker routes that instruction to a liquidity provider or internal book. Once matched against an opposing order, the trade is considered filled. A full fill means the entire requested size was executed at the stated price or within the requested parameters. A partial fill occurs when only part of the order size is matched, leaving the remainder open, cancelled, or filled at a different price depending on order type. Fill quality is a core measure of execution.
How traders use fill
Retail traders care about fills because the printed fill price determines actual cost basis, not the price clicked on the platform. On market orders during liquid sessions, fills typically print at or near the displayed bid or offer. During news releases, thin liquidity periods, or gaps, fills can print materially away from the requested level, a phenomenon known as slippage. Institutional desks routinely break large orders into smaller child orders to avoid moving the market and to harvest better aggregate fills across multiple venues. Retail traders auditing broker quality should pull the trade history and compare requested price to fill price on a sample of trades, paying attention to whether negative slippage dominates or whether positive slippage also occurs.
Common misconceptions about fills
Many retail traders assume the platform price is the fill price. It is not. The platform shows an indicative quote; the fill is whatever the matching engine prints at the moment of execution. A second misconception is that limit orders always fill at the limit price when touched. They do not. A limit order only fills if liquidity is available at that level when your order reaches the front of the queue. In fast markets, price can trade through a limit without filling it. A third error is treating partial fills as broker error rather than a normal feature of order book mechanics in thinner pairs or larger sizes.
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Frequently asked
What is the difference between a full fill and a partial fill?
A full fill means the entire order quantity was executed in a single transaction or aggregated transactions at the requested terms. A partial fill means only some of the requested size was matched, with the remainder either left working, cancelled, or filled at a worse price. Partial fills are more common with large order sizes, in less liquid pairs, or when using limit orders where insufficient counterparty volume exists at the specified level.
Why did my order fill at a worse price than I clicked?
This is slippage, and it happens because the price you see on the platform is indicative, not guaranteed. Between the moment you click and the moment your order reaches the matching engine, the market can move. During high-volatility events such as major data releases or session opens, the bid and offer can shift materially in milliseconds. Brokers operating on a-book or straight-through processing models pass through whatever fill the underlying liquidity provider returns.
Can a limit order get a better fill than requested?
Yes, this is called positive slippage or price improvement. If the market gaps through your limit price, a fair broker should fill you at the better available price rather than the original limit. Not all brokers behave this way; some asymmetrically apply negative slippage while capping positive slippage. Reviewing the broker’s execution policy and auditing actual trade prints against requested levels is the best way to test fill fairness over a sample of orders.
Do market orders always get filled?
In normal liquid conditions, yes. A market order instructs the broker to execute at the best available price, so as long as liquidity exists, the order fills. However, in extreme conditions such as a flash crash, a central bank surprise, or a weekend gap, liquidity can evaporate temporarily and fills may print far from the last quoted price, or in rare cases the order may be rejected if no counterparty is available at any price.
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