Look up the same pair on two reputable sites and you will often get two slightly different numbers. Neither is broken. In most cases neither site is quoting a price that was traded at all — they are each calculating one, and calculating it by a different route.
What a cross rate is
A cross rate is an exchange rate between two currencies derived from their rates against a common third currency, rather than quoted directly.
The arithmetic is a division. If you know that one euro buys 1.08 dollars, and one pound buys 1.27 dollars, then the euro-sterling rate follows: 1.08 divided by 1.27, which is about 0.85 pounds per euro. Those figures are illustrative, but the operation is exactly what happens in practice — the dollar cancels out, and you are left with a price for a pair you never looked up.
Why anyone does this
Because the market is organised around a small number of hubs. An enormous share of currency trading passes through the US dollar, which means dollar pairs have the deepest liquidity and the tightest spreads, while most other combinations are thinly traded or not traded at all.
For a bank, going through the dollar can genuinely be cheaper than trading a minor pair directly: two liquid trades with narrow spreads beat one illiquid trade with a wide one. For a data publisher the reason is simpler still — the source data only exists against a hub currency.
Official publication works the same way. The European Central Bank publishes reference rates for the euro against other currencies. It does not publish a Swiss franc to Japanese yen rate, because that is not its job. Any figure you see for that pair from a European source has been calculated: francs per euro divided into yen per euro.
Why the numbers differ
Five reasons, and they compound.
Different pivots. One source routes a pair through the dollar, another through the euro. Each leg carries its own rounding and its own timestamp, so the two routes land in slightly different places.
Different timestamps. A rate is an instant. If one source struck its inputs at 16:00 CET and another at 17:30, the difference is not an error — the market moved in between. This is the largest cause by far.
Rounding at each step. A published rate is rounded before you ever see it. Divide one rounded number by another and the rounding propagates, which is why a cross rate is always less precise than the two quotes behind it.
Mid versus dealt. Some sources publish a midpoint; others publish something closer to a tradeable quote, with a margin already inside it.
One leg is stale. If one currency's rate is fixed once a day and the other updates continuously, the cross inherits the staler of the two.
How large is the disagreement
For two liquid currencies calculated at a similar moment, typically the fourth decimal — far smaller than any spread you will be charged. For thinly traded currencies, or where one leg is a daily fix, it can reach a few tenths of a percent.
Which sets the practical rule: a discrepancy in the fourth decimal is normal and not worth investigating. A discrepancy in the second is a sign that the two sources are measuring different things — different dates, different directions of quote, or one of them quoting a retail price rather than a reference rate.
Triangular arbitrage, and why it holds this together
If a cross rate drifted meaningfully from the two direct rates behind it, there would be free money: buy the pair one way, sell it the other, pocket the difference. Automated systems watch for exactly this across every triangle of currencies, continuously.
The practical effect is that the discipline is enforced within fractions of a second, which is why cross rates track their components so closely and why the residual differences you see are about timing and rounding rather than genuine mispricing.
What to check before comparing two figures
Four questions settle almost every apparent contradiction:
- Same moment? Compare the timestamps before anything else.
- Same direction? 0.85 and 1.17 are the same rate written two ways.
- Same quotation unit? For the yen or the forint, one source may be quoting per 100 units — see quotation units.
- Reference or offer? A bank's rate and a central bank's reference rate are not comparable and never will be.
The cross rates page here derives every pair from the same set of reference rates, struck at the same moment, with the source and time shown — so any two figures on it are at least measuring the same thing.
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Frequently asked questions
How an exchange rate is actually set, what a spread costs on a real transaction, what happens when your income and your debt are in different currencies, and what to check before paying or being paid abroad. They explain mechanisms rather than forecast rates, and each one carries the date it was last revised at the top.
No. We publish no forecasts, price targets or trading calls, and no article recommends buying or selling a currency. Exchange rates over short horizons are close to unpredictable, and a site that pretends otherwise is selling something. What the articles do instead is explain the mechanism, so that you can read the news for yourself.
They are written by the kursdanas.rs editorial team. We accept no commissioned or sponsored articles, and advertising has no influence on what is published or on the order of anything in our tables. Where an article states a figure it names the source, and where we get something wrong we correct it and change the revision date shown on the page.