No. Saying there's one exchange rate is a fiction. I used to lead the development for currency pricing algorithms for a major market-making investment bank. T

No. Saying there's one exchange rate is a fiction. I used to lead the development for currency pricing algorithms for a major market-making investment bank. Think about the way the market works fundamentally. You have people who want to sell at rate X and people who want to buy at rate Y. These form the basis of the bid/ask pricing, if the values cross then the people involved can do a trade. A retail currency exchange broker will add their spread on-top of the market bid-ask spread, but that doesn't alter the fact that there is a fundamental underlying spread caused by differing views among the buyers and sellers of the currency. There's also not a single market which can have a mid-price. Currencies aren't like stocks where there's a single point where the trades happen. There are lots of currency markets and at any one point in time they'll have different fundamental bid/ask spreads (because of latency), you'll also have differences based upon volume and market depth, who's willing to trade with you, and the participants in that market (many bigger trades now happen in private dark pools). So once you've picked what your definition of market is then you need to pick your definition of midpoint. Are you going to take the middle of the bid-ask, are you going to take the price the last actual trade was done at, or a volume-weighted average price, are you going to filter out momentary spikes, are you going to filter out prices from people who are purposefully market manipulating, etc. What about when there's low liquidity and price might be wildly off ? And that's all stuff that's required to just arrive at a market price. You have to take a subjective view on every-one of these decisions, so in practice any serious market participant is going to have a slightly different view of what the market is for any currency. On the point of offering a fixed single exchange rate, yes it's possible, but the the broker offering it (1) has to make their profit from somewhere other than the spread and (2) take the risk that if the market moves against them that they'll lose money (and again the cost of this has to be covered elsewhere). (2) is actually a huge risk. If the market moves so your price is outside of the market bid-ask range then someone can arbitrage you and make risk free profit from your out of market price and basically bankrupt you. So to defend against this you either need to be able to stop transactions if this ever happens of put enough of a delay in your system so you can make sure this never happens.