Use any reasonable exchange rate source - the key requirement is consistency:
❗️Use one method consistently across all transactions.
• Federal Reserve (H.10) - Daily rates, high reliability, historical data; Excel download available.
• U.S. Treasury (Fiscal Data) - Official U.S. Treasury rates; useful for year-end reporting and balances.
• Investing.com - Daily exchange rates, historical currency data, CSV/Excel downloads, including currently available Russian ruble (RUB) information.
• IRS Annual Rates - Annual averages; simple option for frequent transactions.
• OANDA - Daily & historical rates; widely used in practice.
• XE - Daily/monthly tables; quick reference and historical data.