40 CFR § 713.17 - When to report.
(a) Any person who must report under this part must report for the reporting year described as follows. A reporting year is the year during which mercury activity, required to be reported by this rule, has occurred. The 2018 reporting year is from January 1, 2018 to December 31, 2018. Subsequent reporting years are from January 1 to December 31 at 3-year intervals, beginning in 2021.
(b) All information reported for an applicable reporting year must be submitted on or before the first day of July following the reporting year. The submission deadline for the 2018 reporting year is July 1, 2019. Subsequent submission deadlines are on or before the first day of July following the reporting year, in 3-year intervals, beginning in 2022.
(c) The data from the 2018 reporting year will be used for the 2020 mercury inventory, the data from the 2021 reporting year will be used for the 2023 mercury inventory, and so forth at three-year intervals.