Base and Quote Currency
What are the base and quote currency? The first and second currency in a pair: the price shows how much of the quote one unit of the base is worth.
The base currency is the first currency in a pair; the quote currency is the second. The pair's price answers one question: how much of the quote does one unit of the base buy? EUR/USD at 1.10 means one euro costs 1.10 dollars. Simple as it looks, this convention decides what a chart is actually telling you, which side of a trade you hold, and in what currency you get paid.
How it works
Every FX position is two positions. Buying EUR/USD means buying euros and selling dollars; selling it means the reverse. That is why every fundamental view needs two halves: a pair rises when the base strengthens against the quote, which can come from base strength, quote weakness, or both at once. The cleanest trades are the ones where the two halves agree, a strong base against a weak quote.
The convention also sets the accounting. Profit and loss accrue in the quote currency: one pip on a standard lot of EUR/USD is 10 dollars because the dollar is the quote. And the swap you pay or earn follows the same structure: you earn the base currency's interest rate and pay the quote's.
A worked example
Suppose you expect dollar weakness after a soft US inflation print. "Short the dollar" is not a trade yet; the dollar is the quote in EUR/USD but the base in USD/JPY. To be short dollars you buy EUR/USD (selling the quote) or sell USD/JPY (selling the base). Now add the other half: if the euro's own fundamentals are soft while the yen's are improving, selling USD/JPY expresses the dollar view against the stronger partner, and the same dollar move earns more. Reading a pair always means reading both currencies, and picking the pair is half the trade.
Common mistakes
The classic chart-reading error is seeing USD/JPY fall and calling it "yen down": a falling USD/JPY is the dollar falling against the yen, so yen up. Check which side is the base before interpreting any move. A second, subtler mistake is analysing only one currency of a pair: a perfect bullish case for the base can still lose money if the quote is even stronger. Currencies are always priced relative to each other, never in isolation.
See it in the data
This is why the platform scores each currency separately and then pairs the scores: a trade needs a strong side and a weak side. See how the two halves combine in our guide to how currency pairs price two economies against each other.