Why Currency Exchange Rates Change Every Second
Finance - 3 min read - Published 2026-09-06 - Updated 2026-10-19
Check a currency converter twice in a minute and the rate may have changed. The foreign exchange market is the largest financial market in the world, trading trillions of dollars' worth of currencies every day, according to surveys by the Bank for International Settlements. It runs around the clock on weekdays across financial centers from Sydney and Tokyo to London and New York, and prices move with every trade.
What moves exchange rates
An exchange rate is a price, set by supply and demand for each currency. Demand rises when people and businesses need a currency to buy a country's exports, invest in its companies or property, or hold its government bonds.
Interest rates are among the strongest influences. If a central bank raises rates, deposits and bonds in that currency pay more, which tends to attract investment and strengthen the currency; cutting rates tends to do the opposite. Expectations matter as much as decisions: rates often move on hints about what a central bank will do next.
Inflation erodes a currency's purchasing power over time, so persistently high inflation tends to weaken it. Trade balances, economic growth, political events and general risk mood also play a part. In uncertain times, money often flows to currencies seen as safe, such as the US dollar, Swiss franc or Japanese yen.
Some countries fix or manage their rate instead. The Hong Kong dollar, for example, is kept within a narrow band of 7.75 to 7.85 per US dollar. Such pegs only hold while the central bank has the reserves and will to defend them.
The mid-market rate
In the wholesale market there are always two prices: the bid (what buyers will pay) and the ask (what sellers want). The mid-market rate is halfway between them. It's the rate you see on financial news sites and most currency converters, and the fairest benchmark for comparing what you're actually offered.
Few consumers get the mid-market rate. Banks, card providers, airport kiosks and transfer services usually quote a less favorable rate and keep the difference, sometimes on top of a separate fee.
How hidden markups work
Worked example: the mid-market rate is 1 EUR = 1.10 USD. A provider offers to sell you euros at 1.14 dollars each. To buy 1,000 euros you pay $1,140 instead of $1,100 at mid-market - $40 more, a markup of about 3.6%, even if the provider advertises "no fees".
Compare the offered rate with the mid-market rate at the same moment to see the true cost. Airport and hotel exchanges often have the widest gaps; some banks and specialist transfer services are much closer to mid-market.
Dynamic currency conversion
When you pay by card abroad, a terminal or ATM may offer to charge you in your home currency instead of the local one. This is called dynamic currency conversion, and the rate used is set by the merchant's provider, often with a significant markup. Choosing to pay in the local currency usually means your own card's rate applies instead, which is typically better. The same applies when an ATM asks whether to "accept the conversion".
Paying less when spending abroad
Check your card's foreign transaction fee before traveling; many cards charge around 3%, and some charge nothing. Always choose to pay in the local currency. Withdraw larger amounts less often if your bank charges a fixed fee per withdrawal, and avoid exchanging cash at airports when you can.
For sending money abroad, compare the total amount the recipient will receive across a few services, rather than looking only at the advertised fee - the exchange rate markup is often the larger cost.
Using a currency converter
A converter showing reference or mid-market rates is ideal for estimating prices and checking whether an offer is fair. Rates are typically updated regularly rather than every second, so treat converted amounts as close estimates; the rate you actually pay will include whatever margin your bank or provider adds.