Synthetic Currency Pairs: What the Two Legs Really Cost

Five published explanations of this technique were read in full for this page. Between them they cover what a synthetic pair is, how to assemble one and what it costs, and not one of them mentions margin. A synthetic holds two positions in two separate symbols, and a trading platform margins each of those symbols on its own terms.

Check First Whether the Cross Is Actually Quoted

The whole technique rests on a premise: that the cross a trader wants is not available to trade directly. That premise is asserted in every explanation read here and verified in none of them, and the oldest of those explanations was published in January 2014.

Retail instrument lists have grown since then. A cross that had to be assembled by hand a decade ago may now sit in the platform’s own symbol list, already quoted, already margined once instead of twice.

The check costs a few seconds: open the symbol list and search the three-letter code of each currency in turn, because a platform may file the pair in either direction and under a naming convention that does not match the one in a published article.

Only when the search returns nothing does the two-leg route arise at all. It is worth knowing how currency pairs are classified before running that search, since the classification predicts which crosses tend to be listed and which do not.

A Synthetic Is Two Positions, Not One Pair

The construction itself is simple to state. Two symbols that share a currency are traded in opposite directions with respect to that shared currency, and what remains is exposure to the two currencies that were not shared.

What the construction does not do is create an instrument. After both orders fill, the account holds two ordinary positions. Each has its own ticket, its own entry price, its own floating result and its own margin line.

Nothing on the platform records that the two were opened for a single purpose, and nothing closes them together: two exits are needed, and between the first exit and the second the account is exposed to whichever leg is still open.

The arithmetic relationship between three rates that makes this work is the same one that underlies the triangular relationship between three rates, and that page carries the relationship itself. What matters here is narrower and more practical: the two tickets stay two tickets until each one is separately closed.

Matching the Legs Is a Notional Problem, Not a Lot-Size One

Here is the step the published explanations skip. The shared currency cancels only if the amount of it standing on each side is the same amount. That is a condition on value, and lot size does not express it.

A lot is denominated in the base currency of the symbol being traded, which is the first of the two codes. Two positions of one lot each, in two different symbols, therefore carry equal amounts of two different base currencies. The quantity of the shared currency each one generates depends on that symbol’s exchange rate, and two symbols do not carry the same rate.

Equal lots consequently leave a residue of the currency that was supposed to disappear, and that residue is an open exposure the trader did not intend and is not watching.

Matching the legs means sizing the second position so that the shared-currency value it produces equals the value produced by the first. Two consequences follow. The first is that the required size is rarely a round lot, so the broker’s minimum size increment sets a floor on how accurately the match can be struck at all.

The second is that the match holds at one moment only: as the two rates move apart, the shared amounts stop being equal, and the position drifts back toward carrying a residue unless it is re-sized.

Margin Is Charged on Both Symbols, Whatever the Account Mode

None of the five explanations read for this page mentions margin, which is the cost that decides whether the route is affordable at a given account size.

The MetaTrader 5 margin documentation sets out how the requirement is computed, and the structure of that documentation answers the question directly.

Margin is calculated per symbol, from the contract specification belonging to that symbol. The provision that reduces a requirement when opposing positions are held, described there as a basic calculation or a calculation on the larger leg, is itself a field inside a symbol’s contract specification.

A relief defined inside one symbol’s specification has no reach into another symbol. The two legs of a synthetic are, by construction, two different symbols, so each is margined from its own specification and the account carries the sum of the two requirements.

Choosing a different account mode does not change this either, because netting resolves positions within a symbol rather than across symbols; the distinction between netting and hedging position accounting is a question about repeated positions in one instrument, and a synthetic is one position in each of two.

The Costs That Recur: Two Spreads and Two Swap Lines

Three of the five explanations state or imply that a synthetic costs roughly what the direct cross would cost. None of them sources that claim, and the structure of the position argues against it.

Two positions are opened, so two spreads are crossed at entry, and two more are crossed when the legs are closed. The relevant comparison is not one spread against one spread but the sum of both legs against whatever the direct cross would have charged, and that sum is what the spread actually is on each of the two symbols involved.

Financing behaves the same way. Each leg accrues its own overnight charge or credit at each rollover, computed from its own symbol. The two lines have their own signs and their own sizes, and they do not resolve into the single figure the direct cross would have applied.

Over a holding period measured in weeks, this is the cost that compounds, and the mechanics of the swap charged on a position held overnight apply twice over rather than once.

What the Turnover Data Actually Says About Thin Crosses

Every share and count figure in the five explanations is uncited. One states a percentage for the share of the market held by dollar pairs; another states how many pairs exist and how many are quoted, and the encyclopedia entry carrying that second claim flags it on its own page as needing a citation.

The distribution is published, and it is published by the Bank for International Settlements. Its April 2025 survey of over-the-counter turnover puts the US dollar on one side of 89.2 percent of trades. The equivalent reading three years before was 88.4 percent.

The euro follows at 28.9 percent, the yen at 16.8 percent and sterling at 10.2 percent. Shares are counted against a total of 200 percent, because every trade involves two currencies.

What that supports is the reason the technique uses dollar legs at all: depth is concentrated where the dollar is, so the two symbols a trader assembles a cross from are almost always the two dollar pairs. What it does not support is any specific count of how many crosses a broker quotes, which is a fact about one broker’s instrument list and is settled by reading that list.

When the Two-Leg Route Is Worth Taking

Three conditions have to hold together. The cross must be genuinely absent from the instrument list rather than filed under an unexpected name. The intended holding period must be short enough that two financing lines do not overtake the reason for the trade. And the intended size must be large enough that the second leg can be matched within the broker’s minimum increment.

Where any one of those fails, the route costs more than it returns. A quoted cross makes it redundant. A long hold hands the position to the financing lines. And a size near the platform minimum cannot be matched accurately enough for the shared currency to cancel, which leaves a residual exposure that can easily exceed the exposure the trade was opened for.

Who Should Not Use This Route

An account trading at or near the minimum lot size cannot strike the match this construction depends on. Anyone who wants a single position with one stop level, one financing line and one margin figure is describing the directly quoted instrument, and the answer in that case is to trade a cross the broker lists.