Last look — why a liquidity provider can reject your order

You click "buy" on EUR/USD at 1.0850, and instead of a fill confirmation you see a rejection or a fresh, worse quote. Poor connectivity is not always to blame. Sometimes it is last look — a fraction of a second in which the liquidity provider checks whether the price it offered is still worth honouring, and only then accepts or rejects your order. The mechanism has a genuine rationale, but it can be abused. Below I explain how it works, why it exists, and why it stirs so much controversy among retail traders.

What last look actually is

Last look is a practice used in electronic trading where a liquidity provider — a bank, a market maker or another price-quoting entity — receives your order at a quoted price and then takes a short window of time for a final check before deciding whether to accept the trade or reject it. That window typically lasts from a few to a few dozen milliseconds. During it the provider verifies two things: that the order is technically valid (a validity check) and that the price it showed still matches the current market (a price check).

The key difference from an exchange-traded market is that on a classic exchange an order hitting a matching quote is executed instantly and unconditionally. In a last look model the provider's quote is, in practice, an invitation to trade rather than a binding offer — the final word belongs to the entity quoting. For you this means the price on your screen is not a guarantee of execution. Between your click and the confirmation stands a decision by the other side.

Why the window exists at all

The argument for last look is serious and worth understanding before you write the mechanism off as pure malpractice. A liquidity provider quotes prices to many clients across many platforms at once. In a world where information moves faster than its own systems can refresh a quote, it is exposed to latency arbitrage — a situation where a faster participant trades on a price that is already stale before the provider can pull it. Last look gives it a moment to catch such a case and protect itself against so-called toxic order flow, a stream of trades that systematically exploits its latency.

From that protection flows a promised benefit for the market. If a provider can reject a trade on a stale price, it carries less risk, and less risk lets it quote tighter spreads. Supporters therefore argue that the mechanism gives every client tighter prices while the cost falls mainly on those trying to game the delay. That is a real argument, but its strength depends on how honestly last look is applied.

Where the controversy hides — asymmetry

The problem starts with asymmetry. Imagine that during the last look window the price can move either way. If the move favours the liquidity provider (and works against you), the trade is accepted — the provider is happy to take the rate that suits it better. If the move favours you, the trade is rejected, because the entity quoting does not want to fill at a price that has just turned unfavourable for it. The client ends up with heads I win, tails you lose, in the version where the client is the losing side.

For a retail trader this asymmetry shows up in ways familiar from the platform: repeated requotes, rejected orders in moments of fast movement, and one-sided price slippage — slippage that lands against the client surprisingly often. It is hard to prove in any single case, because each rejection on its own has an explanation. Only the statistics of many trades reveal whether the last look window is applied symmetrically or one-sidedly. It is also worth separating this mechanism from the alleged hunting of stop-loss orders — two distinct phenomena, though both bear on execution quality.

"Last look should be used for the price and validity checks only, and for no other purpose." — FX Global Code, Principle 17, Global Foreign Exchange Committee, 2021.

A hypothetical example — what one rejection looks like

Let us trace it through numbers. This example is hypothetical and only illustrates the mechanics. A trader clicks to buy EUR/USD at 1.0850, and the liquidity provider opens a last look window 50 milliseconds long. During that time the market drifts a little. If the rate ticks to 1.0849 — in the trader's favour, since they could buy cheaper — the provider rejects the order and offers a requote at the new price. If instead the rate ticks to 1.0851 — in the provider's favour — the trade is accepted at the original 1.0850, even though the market has already moved on.

Notice what happened here. When the move favours the client, the last look window "protects" the provider from a worse price for itself; when the move works against the client, the same window stays silent and lets the trade go through. If that logic runs consistently in one direction, the client pays a hidden cost that never shows up in the spread table. A symmetric last look would reject trades on moves of the same size in both directions; an asymmetric one rejects mainly when the entity quoting would lose. Which version your provider uses is a question of fairness, not of technology.

What the rules say

Last look does not operate in a regulatory vacuum. The central document is the FX Global Code — a set of good-practice principles for the wholesale foreign exchange market, developed by the Global Foreign Exchange Committee with the participation of the major central banks. Principle 17 of the Code regulates last look directly: it is meant to be a risk-management tool serving only the price and validity checks, not a way to peek at which direction the market will take. The Code prohibits using information from the last look window to trade on one's own account ahead of the decision to accept the client's order.

The UK regulator, the Financial Conduct Authority, confirmed its recognition of the updated Code in 2021 and stressed that prolonging the last look window in order to see where the price will go is inconsistent with the principles. The FCA also requires market participants to disclose clearly whether they apply symmetric or asymmetric last look. That is an important point: neither the Code nor the regulator bans the mechanism itself — they accept its rationale — but they demand transparency and prohibit specific abuses. The line between a permitted protection tool and prohibited front-running lies precisely in what happens during those few dozen milliseconds.

Where you will meet last look, and where you will not

Last look appears mainly in the wholesale foreign exchange market and on ECN-style platforms built on multiple liquidity providers, where prices come from banks and market makers competing for your order. A "true" market with no last look, in which every quote is binding, does exist, but it is rarer and more costly for the provider to maintain. The mechanism is therefore the rule rather than the exception in the infrastructure underpinning retail currency trading. It helps to understand how the wholesale interbank market works and how the ECN model differs from the market-maker model. The broader regulatory backdrop sits in the regulations section on forexmechanics.com.

The retail catch is that you usually do not know whether your broker, or the liquidity provider behind it, applies last look, and if so in which version. That information is often buried in execution-quality documents or absent altogether. So the best tool is not theory but a concrete question put to the broker and an analysis of your own rejection history. And to be fair: last look is not fraud by definition. It has a real rationale in protecting the entity quoting, and it is often applied fully in line with the Code. The line between protection and abuse is thin, however, and the one thing that holds it in place is transparency.

What to do tomorrow

1. Put one concrete question to your broker. Write on chat or by email: "Is last look applied to the execution of my orders, and if so, is it symmetric or asymmetric, and what is the typical window length?" Save the answer. The absence of a clear reply is itself information about how transparent that broker is.
2. Review your own rejection history from the past month. Open the trade report in your platform and count how many orders were rejected or requoted, and at which moments it happened. If the rejections cluster around fast moves in your favour, you have grounds to look closer and to raise the matter with your broker.
3. Check the execution-quality documents. Go to your broker's website and find the order execution policy and any liquidity-provider disclosure sheet. Look for the words "last look", "price check", "symmetric" and "asymmetric". What a broker declines to disclose tells you more than what it advertises.
4. Compare execution quality across two accounts. Open an account with a second broker on a different execution model and run the same orders through both, at the same hours, for two weeks. The difference in the number of rejections and in slippage will show you in practice what no marketing will — which infrastructure genuinely treats your orders better.