Indiana Code Title 6. Taxation § 6-1.1-3-1.5

Sec. 1.5. As used in this chapter, “filing date” refers to the day in a year on which a personal property tax return is due for a particular assessment date in that year (disregarding any extension period that may be granted for the filing of the return and any period in which an amended return may be filed).  The filing date is May 15.