Exchange-rate data sources
Last reviewed: 1 November 2026
Rateory uses the Frankfurter v2 API for current and historical reference-rate data. Frankfurter aggregates reference data from central banks and other official institutions. Rateory uses the API as a comparison baseline; it does not treat the returned value as a guaranteed bank, card, cash-exchange or money-transfer quote.
What Rateory displays
The converter shows the source currency, target currency, calculated result and the provider date returned with the reference rate. Historical charts use the same reference-data service so that current and historical comparisons are based on a consistent source.
Frankfurter data is generally published on a daily reference basis rather than as tick-by-tick tradable market pricing. A rate can therefore remain unchanged outside source publication periods, including weekends or holidays.
Blended reference data
Rateory does not label a Frankfurter value as the rate of one specific central bank unless that attribution is explicitly available. Where the upstream service combines official-source observations, the resulting figure should be read as a reference value supplied by Frankfurter, not as an executable quote from the underlying institution.
Bulgarian lev legacy handling
For legacy BGN conversions after Bulgaria’s euro adoption, Rateory uses the fixed conversion relationship of 1 EUR = 1.95583 BGN. Cross-rates involving BGN can be derived through EUR and are labeled in the application logic as legacy or derived values rather than live BGN market quotes.
What the data does not include
- Provider-specific exchange-rate margins or spreads.
- Card foreign-transaction fees, transfer fees or intermediary-bank charges.
- Cash-market availability or local payout conditions.
- A promise that a displayed rate can be executed at a bank, broker or transfer service.
Availability and corrections
Upstream reference data can occasionally be delayed, missing or revised. Rateory does not invent a missing historical point. If you believe a displayed value or explanation is wrong, follow the Corrections Policy or contact [email protected].
For calculation details and practical comparison guidance, read the Rateory methodology.