What the conversion costs

Row 01The cost has two possible parts, and one of them hides

The cost of a conversion is made of up to two things: a margin inside the rate, and an explicit fee if the terms charge one. The margin is the gap between the effective rate and the mid-rate, and because it is inside the rate it is not itemised — it simply makes the amount you receive smaller. The explicit fee, where it exists, is a named charge and appears as a line. Most accounts rely on the margin alone; some add a fee as well; a few charge the fee instead of the margin. To know which you are paying, the statement or the terms must show it, and a conversion with no visible fee is not necessarily free — it usually just means the cost is in the rate.

Row 02How the cost scales with the amount

Because the margin is a percentage, the cost scales roughly with the amount converted. A 1.5 percent margin costs about 1.50 on 100, about 15 on 1,000 and about 150 on 10,000. That linear scaling is why small conversions cost little in absolute terms and large ones cost a lot, even at the same headline margin. It is also why a fixed explicit fee behaves differently: a flat fee is a larger share of a small conversion and a smaller share of a large one, so the cheapest structure depends on the size. The arithmetic below makes the percentage concrete; it is illustrative, and the real margin depends on the operator, the method, the corridor and the moment.

Row 03Why the corridor and the method change the margin

The margin is not one number for all currencies. Liquid, widely traded pairs — dollars, euros, pounds — carry narrower margins because the underlying market is deep and cheap to transact. Exotic or thinly traded currencies carry wider margins, because the processor or bank has more cost and more risk in handling them. The payment method matters too: a card scheme applies its own margin on its leg, while a bank transfer may apply a different one, and a crypto leg converts at a valuation point that behaves differently again. The consequence is that the same person converting the same amount can pay different margins depending on which currency pair and which method is used, which is why the corridor is a first-order part of the cost, not a detail.

Row 04How to measure the cost of a conversion you already made

Measurement is arithmetic on two numbers you can obtain: the effective rate from the statement or account history, and the mid-rate at the same moment from a reference source. Express the difference as a percentage of the mid-rate, and that percentage is the margin you paid. Multiply it by the amount converted for the money. If the amount you received is shown rather than the rate, the same figure is derivable: the gap between what the mid-rate would have produced and what you received, divided by the mid-rate amount, is the cost. This is the only way to see a cost that is otherwise inside the rate, and it is the number worth comparing between operators rather than a quoted “0 percent fee” claim.

• Get the effective rate From the statement or the account history, for that specific conversion.
• Get the mid at that time From a reference source for the same currency pair and moment.
• Divide the gap by the mid The result is the margin as a percentage — the true “conversion fee”.
• Multiply by the amount That gives the cost in money for that conversion.

Row 05When there is an explicit fee as well

Where the terms charge an explicit conversion fee, the total cost is the fee plus the rate margin, and both are real. An explicit fee is easier to see, which can make an account that charges one look more expensive than an account that hides a wider margin in the rate — but the comparison is between totals, not between the visible parts. The honest way to compare two accounts is to compute the full cost of the same conversion on each: the effective rate against the mid, plus any settled fee. A “no conversion fee” headline describes the absence of an explicit fee line, not the absence of a margin in the rate.