How do I calculate the maximum account value to report on the FBAR?

For each foreign account, you report the highest balance the account reached at any single point during the calendar year, not the year-end balance or an average. Review your monthly or quarterly statements and pick the peak. Convert that peak from the foreign currency to U.S. dollars using the Treasury Reporting Rates of Exchange for December 31 of that year, published by the Bureau of the Fiscal Service on fiscal.treasury.gov. If you cannot pin down an exact figure, FinCEN allows a reasonable estimate, but you must check the box indicating the value is not precisely determined. Report every account that individually or together pushed your total over $10,000, even small ones. When in doubt, report; the FBAR is informational and reporting an extra account costs you nothing.