Best Execution Explained: How FX and CFD Brokers Handle Your Order

Imagine you place an order to buy euros on a Tuesday morning. Your platform shows one price, but by the time your click lands, the number has shifted slightly. That small gap has a name — slippage — and the rules around it, and around how your broker handles your order, are what "best execution" is all about. It is one of the quieter obligations in retail trading, but arguably one of the most practical.

Let's unpack it over a cup of chai.

What best execution actually means

Best execution is the duty on a firm to take all sufficient steps to get the best possible result for clients when executing orders. That's how the UK's Financial Conduct Authority (FCA) frames it. In the European Union, Mifid II Article 27 puts it in terms of "total consideration" — meaning the price of the instrument plus every cost directly tied to execution, such as execution venue fees, clearing and settlement fees, and any other charges paid to third parties.

Note that it is a duty of effort, not a promise of outcome. No regulator guarantees you'll get the perfect fill. What the rules require is a thoughtful, documented, monitored process — and disclosure so you understand it.

The execution policy: your broker's rulebook

Under Mifid II, investment firms must give clients appropriate information on their order execution policy. The policy has to explain clearly, in enough detail and in a way clients can easily understand, how orders will be executed. Firms must also obtain your prior consent to the policy. And if orders might be executed outside a trading venue — that is, off-exchange — the firm must tell you and get your prior express consent, either as a general agreement or transaction by transaction.

In plain terms: you should be able to read, before you trade, where your orders go and how the broker picks the place to send them. If that document reads like it was written by a committee of lawyers who were late for lunch, that's a signal to ask questions.

Venue selection and why it matters

Markets rarely have one place to trade. When more than one competing venue can execute your order, Mifid II requires firms to compare the results they'd achieve on each eligible venue listed in their policy — taking into account their own commissions and the costs of executing on each. That comparison sits at the heart of venue selection.

The FCA's multi-firm review of wholesale banks in UK listed cash equities offers useful colour here, even though it focuses on a different corner of the market. It noted that firms increasingly rely on execution algorithms and smart order routing technology, and that liquidity has been moving toward bilateral trading, including systematic internalisers (SIs) — firms that match client orders against their own book. The review found no evidence that internalisation was damaging client outcomes, but it was explicit that internalisation does not automatically guarantee best execution. Where a firm acts as counterparty, potential conflicts of interest have to be managed.

How monitoring actually works

Rules are one thing; watching them work is another. Article 27 requires firms to monitor the effectiveness of their execution arrangements and policy, identify deficiencies and correct them where appropriate. Firms must regularly assess whether venues in their policy deliver the best possible result, and must notify clients with an ongoing relationship of any material changes.

The FCA review described how monitoring looked in practice: a combination of real-time alerts and post-trade analysis. Real-time monitoring typically looked at prices and volumes across venues, platform availability and connectivity, and client order preferences. Post-trade monitoring measured outcomes across execution factors — price, costs, speed, likelihood of execution and settlement, size, and the nature of the order. One widely used metric was implementation shortfall, the difference between the price when the broker receives the order and the final execution price.

Good practice went further. One bank built a proprietary composite score for each trade, factoring in market conditions and multiple execution factors, then investigated the largest deviations in both directions. That is monitoring used as a learning loop rather than a box-tick.

Price slippage: what the US rules say

In the United States, the National Futures Association (NFA) sets detailed requirements for Forex Dealer Members — firms acting as counterparties to retail forex customers. Its guidance tackles slippage directly. Slippage sometimes occurs between the moment a customer submits an order and the moment it reaches the dealer's system. Some dealers requote the current price and ask the customer to confirm; others build in slippage parameters that permit execution if the slippage is within set limits.

Crucially, dealers using slippage parameters must apply those settings uniformly regardless of which way the market has moved. If a dealer requotes when the market moves against it, it must requote when the market moves in its favour. Customers must receive full written disclosure of the policy before trading.

The NFA is equally direct about marketing. A firm may not claim "no-slippage" or guaranteed fills unless it can demonstrate that all orders for all customers were executed at the price initially quoted, and it has no authority to adjust accounts in a way that changes the executed price. If it advertises no slippage, it must prominently disclose that transmission delays might still result in execution at a different price.

Transparency you can ask for

US retail forex customers have a notable right: on request for a particular executed transaction, the dealer must provide, within 30 minutes, transaction data for the 15 trades immediately before and after in the same currency pair. That includes execution date and time to the nearest millisecond in Eastern time, quantity, execution price including any mark-up, and commissions or other charges. Dealers must also inform customers of this ability via notices on their website, trading platform and confirmation statements.

Per-trade confirmations must disclose commissions and fees; where straight-through processing is used, any mark-up or mark-down on the offsetting position; and where it isn't, the mid-point spread cost — defined as the difference between the execution price and the mid-point of the bid/offer spread when the order was received.

Enforcement and governance: where it gets real

Obligations have teeth through supervision. The FCA review found stronger practices than in its 2014 thematic work, and monitoring that could identify good and poor outcomes, with evidence of firms acting on poor ones. But it also found variable management information for senior managers and the least progress in governance — specifically, weak challenge from the second line of defence. At some banks, compliance lacked the data and tools to independently assess outcomes; the strongest examples saw compliance checking price alerts daily, comparing prices across venues and flagging trades executed away from the prevailing best bid and offer.

The review also cautioned against assuming all is well because clients stay. Senior managers at some firms relied unduly on client retention as an indicator of best execution. A quiet complaint inbox is not proof of good execution — it may just be proof of a quiet inbox.

In the US, the NFA's rulebook prohibits dealers from cancelling or adjusting the price of executed customer orders except in narrow circumstances — for example, resolving a customer complaint in the customer's favour, or where a straight-through-processing counterparty adjusts and the dealer notifies the affected customer within 15 minutes and applies the change consistently. Separately, the CFTC has approved NFA rule amendments and an interpretive notice enhancing protections for retail forex customers, including additional capital requirements, risk management programmes and extra market disclosures on dealer websites.

Jurisdiction matters — a lot

This is where you should slow down. The EU's Mifid II framework, the UK's COBS rules, and the NFA and CFTC regime for US retail forex are separate systems with different scope, terminology and enforcement. The FCA has said it received feedback on the scope of best execution rules and requirements for express consent, and will consider that in any future review; it has also said it would consult on possible rule changes in the first half of 2026 if appropriate. The NFA's requirements apply to its members, and its forex rule has been amended many times. Details can and do change, and rules that apply to one firm may not apply to another.

So treat this as orientation, not legal advice. If you want to know what protections apply to your account, the honest answer depends on where you live, where the firm is regulated, and what kind of firm it is.

What you can do with this

Read your broker's execution policy before you trade, not after. Notice whether it explains off-venue execution and how you consent. Ask how slippage is handled and whether settings apply in both directions. If you're in the US retail forex market, know that you can request surrounding transaction data — and that firms must tell you so. And remember the underlying logic: best execution is a process of comparison and correction, not a magic number. Understanding it won't make slippage disappear, but it will help you judge whether your broker is doing the work.