Exchange rate data looks simple – a currency code and a number – but every value carries assumptions: which side of the pair is the base, which moment it represents, whether a markup is included, and which code was valid on that date. These articles explain those assumptions in plain English, with examples you can run against the fxapi API.
FX glossary
| Term | Definition |
|---|---|
| Exchange rate API | A web service that returns currency exchange rates as JSON over HTTPS – how it works, e.g. the fxapi foreign exchange rates API. |
| Mid-market rate | The midpoint between bid and ask prices; a neutral benchmark without markup. |
| Bid / ask spread | The gap between the price a dealer pays and the price it charges for a currency. |
| Base currency | The currency that counts as one unit in a rate, e.g., EUR in EUR/USD. |
| Cross rate | A rate between two currencies calculated through a third, usually USD. |
| ISO 4217 | The standard defining three-letter currency codes, numeric codes and minor units. |
| Minor unit | The number of decimal places a currency uses: 2 for USD, 0 for JPY, 3 for KWD. |
| Closing rate | The spot rate at the end of a reporting period, used for balance sheet items. |
| Average rate | The mean of rates over a period, often used for income and expenses. |
| End-of-day rate | One representative value per day, taken at a defined cut-off (UTC for fxapi). |
| Currency peg | A regime that holds a currency at or near a fixed rate against an anchor. |
| Redenomination | Replacing old currency units with new ones at a fixed ratio, often with a new code. |
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Frequently asked questions
Where should I start if I'm new to exchange rate data?
Read what is an exchange rate API first. It covers how requests and responses work, the main data types and how to evaluate a provider; the other articles go deeper on individual concepts.
Are these articles financial or accounting advice?
No. They explain concepts for developers and analysts. For accounting treatment, follow your policies, your auditor and the standards themselves; nothing here is investment advice.
How do I try the concepts with real data?
Create a free key at app.fxapi.com/register. The Free plan includes 300 requests per month with latest, historical, fluctuation and average rates, so you can run every example in these articles.