TLDR: Amounts in foreign currency must be converted into euros using the exchange rate published in the Official Journal of the European Union known on the first day of the month of receipt. A simplification is allowed if the taxpayer uses a single currency for its accounting.
Legal basis and general principle
The conversion rule is explicitly provided for by Article 299 quinquies of the French General Tax Code (CGI). This text requires the application of the official EU exchange rate known on the first day of the month in which the receipt occurs.
Mandatory conversion method
For each amount received in foreign currency, you must apply the exchange rate of the first day of the month of receipt, as published in the Official Journal of the European Union. This rate is unique for all transactions carried out in the same month.
Special case: simplification for taxpayers using multiple currencies
If you use multiple currencies and convert them into a single accounting currency, you may apply the conversion for the TSN from this single currency. This simplification avoids converting each amount individually from its original currency.
Scope of the rule
The conversion applies to all taxable amounts received in foreign currency, without distinction according to the category of taxable service (digital intermediation or targeted advertising).
Exclusions and limits
No other conversion method (average rate, rate on the day of receipt, etc.) is authorized for the TSN. The specific rules for other taxes or duties do not apply.
Declarative obligations
The converted amounts must be declared in euros as part of the obligations related to the TSN. No exemption is provided for currencies not covered by the official EU rate.