Which currency conversion rate should I use for Form 8938 versus the FBAR?

Both forms generally use the U.S. Treasury Reporting Rates of Exchange published by the Bureau of the Fiscal Service for the last day of the tax year, found on fiscal.treasury.gov. The IRS instructions for Form 8938 direct you to that Treasury year-end rate unless no Treasury rate exists for your currency, in which case you use another publicly available, verifiable rate. The FBAR instructions point to the same Treasury year-end rate. Using a consistent, documented source protects you if questioned. Keep a screenshot or printout of the rate you applied and the date. For asset values that peaked mid-year, you still convert the peak using the year-end rate, which can feel counterintuitive but matches the instructions.