12 Pa. Code § 151.2
Under section 502(c)(2)(iv) of the act (53 P.S. § 6924.502(c)(2)(iv)), every taxpayer who has filed the declaration of taxpayer's estimated net profits required under section 502(c) of the act and who anticipates additional net profits not previously declared or has overestimated anticipated net profits shall file, on or before April 15 of the current year, July 15 of the current year, October 15 of the current year or January 15 of the succeeding year, whichever date next follows the date on which the taxpayer first anticipates the change in antici-pated net profits, an adjusted declaration of estimated net profits and pay to the resident tax officer on or before the quarterly payment dates that remain after the filing of the adjusted declaration, beginning with the quarterly payment date in which the adjusted declaration is filed, equal installments of the tax due as reported on the adjusted declaration of estimated net profits.
12 Pa. Code § 151.2