Exchange-rate margin calculator See what a currency conversion really costs, beyond any headline fee
Almost no one gives you the mid-market rate. The gap between it and the rate you’re actually quoted is the margin — usually the biggest cost of a conversion, and the one nobody shows you. Put in three numbers and this tool works it out, in money and as a percentage.
Enter a positive amount and two positive rates to see the result.
How to use it
Find the live mid-market rate for your pair from a neutral source and note the time, because it moves. Get the provider’s quoted rate (or reverse it from the all-in amount they’ll give you). Enter your amount and both rates. The “margin” is the difference between what the honest midpoint would give you and what you actually get — the true cost, whether or not a separate fee is also charged.
What the result does and doesn’t mean
The percentage lets you compare any two providers, in any currencies, on one honest scale — a bank, an app, a bureau or an exchange. It does not include a separate flat fee if the provider charges one on top; add that yourself for the full picture. And it’s only as accurate as the rates you type: this tool does nothing but arithmetic on your inputs. It holds no live rates and makes no promises about what you’ll be offered.
Rates change every second. Use figures from the same moment for a fair comparison, and always confirm the final all-in amount on the provider’s own page before you commit.
The formula, in plain words
The tool multiplies your amount by each rate to get two totals: what you’d receive at the honest midpoint, and what you actually receive at the quoted rate. The margin is the difference between those two totals. To turn it into a percentage, it divides that difference by the mid-rate total — so the number is the share of the conversion the provider keeps, not a share of some fee you can see. Nothing else goes into it: no live data, no assumptions about your provider.
A worked example
Say you’re converting 1,000 units at a mid-market rate of 1.0850, and the provider quotes you 1.0610. At the midpoint you’d get 1,085.00; at the quoted rate you get 1,061.00. The margin is 24.00 in the target currency, and 24.00 ÷ 1,085.00 works out to about 2.21%. That 2.21% is the real cost, even if the provider advertises “zero commission.” Run the same amount through a second provider quoting 1.0770 and the margin falls to 8.00, or roughly 0.74% — a threefold difference on the identical trade, visible only once you put both on the percentage scale.
When this number matters — and when it doesn’t
The percentage is the figure to carry between providers, because it strips out the amount and the currencies and leaves one comparable cost. It matters most on larger conversions and on anything you do repeatedly, where a percentage point compounds into real money. It matters less on a one-off conversion of pocket change, where a flat fee may dwarf the margin. Two limits are worth naming. If a provider also charges a separate flat fee, this tool doesn’t see it — add it yourself for the all-in picture. And the result is only as honest as the mid-rate you feed it: pull the midpoint and the quote from the same moment, because a stale mid-rate can invent or hide a margin that isn’t really there.
Common mistakes
- Comparing a mid-rate from one moment against a quote captured minutes later, so market drift is mistaken for margin.
- Reading “no commission” as “no cost” — the margin is usually the larger charge and hides inside the rate.
- Forgetting to add a separate flat or fixed fee on top of the margin when the provider levies one.
- Using a rounded or headline rate instead of the actual quoted rate, which understates what you really pay.
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