The account opening form asks for a base currency and offers a short list. Most traders pick their home currency without much thought, or pick the dollar because the instruments they intend to trade are quoted against it. Either choice can be right. What makes it worth a moment's attention is that the decision cannot usually be reversed without opening a second account, and that it sets a cost which recurs on every settlement for as long as the account exists.
What the base currency decides
- The currency your balance, margin and profit and loss are reported in.
- Whether each closed trade needs a conversion, and at what markup.
- What you pay to fund and withdraw from the account.
- How much of your equity moves when the exchange rate moves and you have no position open.
Where the conversion happens
A profit or loss is realised in the quote currency of the instrument. Close a EUR/USD position and the result is in dollars. Close a EUR/GBP position and it is in pounds. Close a Japan 225 index CFD and it is in yen. If your account is denominated in euros, each of those results must be converted before it can be added to your balance, and the broker performs the conversion at a rate of its choosing.
That rate is normally the prevailing market rate plus a markup, disclosed as a percentage in the fee schedule. Figures between 0.3% and 1% are common in the retail market, though some brokers apply a spread rather than a percentage and some do not disclose the mechanism at all beyond a general clause in the client agreement.
The conversion is on the result, not the position
You are not charged a conversion on the notional value of the trade. The charge applies to the realised profit or loss, and to any commission or financing booked in another currency. A losing trade is converted too, which means the loss debited to your account is slightly larger than the loss in the quote currency.
The arithmetic on a normal year
Suppose you trade instruments quoted in dollars from a euro account, close two hundred positions in a year, and average a result of 120 dollars per position in absolute terms — some wins, some losses. That is 24,000 dollars passing through conversion. At a 0.5% markup, the conversion costs 120 dollars over the year. It does not appear as a fee line anywhere; it is absorbed in the exchange rate applied to each settlement.
The figure scales with turnover and with the absolute size of results, not with net profitability. A trader who breaks even on a large number of trades still pays it in full. That is the uncomfortable property of conversion cost: it is charged on gross activity, like the spread, rather than on outcome.
Deposits and withdrawals
The second conversion happens at the boundary of the account. Fund a dollar account from a euro bank account and someone converts: either your bank, your card issuer, the payment provider, or the broker. Each of them applies its own markup, and the one that does it is often decided by which currency the payment is presented in rather than by any choice you make.
Card deposits are the most opaque case. A card issuer converting on your behalf typically applies a markup of its own, on top of any the broker applies, and the transaction appears on the statement as a single figure with no breakdown. Bank transfers in the account's own currency avoid the problem entirely, which is why a matching currency pair between bank account and trading account is worth more than a fractionally better spread.
Dynamic currency conversion is expensive
If a payment page offers to charge you in your home currency rather than the merchant's, that is dynamic currency conversion, and the rate is set by the payment processor rather than by your bank. It is almost always worse. Choose to be billed in the account currency and let your own bank convert.
Choosing a base currency
Three considerations decide it, in this order.
First, the currency you fund and withdraw in. Every mismatch here is converted twice — once in, once out — and this is the largest and most avoidable cost. A trader paid in pounds who funds from a pound account should have a strong reason before opening a dollar account.
Second, the currency your instruments settle in. If you trade dollar-quoted instruments almost exclusively, a dollar account removes the per-trade conversion. This matters more the higher your trade count.
Third, the currency in which you think about risk. An account denominated in a currency you do not spend has a floating value in your own terms. A euro trader holding a dollar account has an unhedged currency position equal to their entire balance, whether or not any trade is open, and a 5% move in the pair changes their real-world wealth by 5% without a single trade being placed.
A short decision procedure
- Write down the currency of the bank account you will fund from and withdraw to.
- List the instruments you actually intend to trade and note their quote currencies.
- If both point at the same currency, that is your answer.
- If they conflict, weigh the per-trade conversions against the deposit and withdrawal conversions using your expected trade count.
- Check whether the broker offers a sub-account in a second currency rather than forcing one choice.
- Confirm the conversion markup in the fee schedule before opening, not after.
Exotic base currencies
Brokers serving many markets often offer local base currencies. These are convenient for funding and remove the deposit conversion entirely, which is a real benefit. They come with two costs worth knowing about.
The first is that every trade in a dollar-quoted instrument now needs conversion, so the per-trade cost rises even as the deposit cost falls. The second is that some brokers apply a wider markup on less liquid account currencies, and a few restrict which instruments or account types are available in them. The fee schedule states this, usually in a table rather than in prose.
How to verify what you are actually paying
The statement will not label conversion as a cost, so it has to be inferred. Take a closed trade whose result you can compute exactly in the quote currency, find the amount credited in your account currency, and divide. Compare the implied rate against the market rate at the moment of settlement. The gap is the markup, and it should match the fee schedule.
Doing this once, on a single trade, is enough to know whether the disclosed figure is the figure being applied. It is one of the few broker claims a client can verify independently and precisely.
Common questions
Can I change my account's base currency later?
Rarely. Most brokers require a new account, since the balance, history and reporting are all denominated in the original currency. Some allow a second sub-account under the same client profile, which is the practical workaround.
Does a multi-currency account remove the cost?
It removes the settlement conversion for the currencies it holds, which helps if you trade instruments in several quote currencies. It does not remove the deposit and withdrawal conversion unless you can fund each currency separately.
Is the conversion charged on losses too?
Yes. The markup is applied to the absolute amount converted, so a loss arrives at your account slightly larger than it was in the quote currency. This is why the cost tracks turnover rather than profitability.
Which is cheaper, a dollar account or my home currency?
It depends on where the volume is. If most of your money movement is deposits and withdrawals in your home currency, that wins. If most of it is trade settlements in dollars, the dollar account wins. Count both before deciding.
