There is never one exchange rate. The mid market price of a currency pair is just an average of the bid and offer prices. The bid price being what trader are wi

There is never one exchange rate. The mid market price of a currency pair is just an average of the bid and offer prices. The bid price being what trader are willing to buy at and the offer price is what people are willing to sell at. The bid and the offer price should never be the same. If they were the same a trade should have happened. So if the mid market for EUR/USD is 1.2993 the prices could be something like bid 1.2990 / offer 1.2996. So when you walk into a bank (if they are giving you the real bid offer) and try and convert USD to EUR you are selling so you will get 1.2990 USD per 1 EUR. And if you were trying to convert EUR to USD you would pay 1.2996 USD for each EUR. There are also many othe factors that will increase costs in these transactions. Banks charge fees to other banks for each trade and they will also show different spreads to different banks based on credit risk and/or volume.