S.C. Code Ann. § 12-16-1110 — When tax is due; extensions; filing requirements; interest

(A) The tax imposed under this chapter is due and payable no later than nine months from the date of the decedent's death.
(B) The personal representative of every estate subject to the tax imposed by this chapter who is required by the laws of the United States to file a federal estate tax return shall file with the Department of Revenue, on or before the date the federal estate tax return is required to be filed: (1) a return for the tax due under this chapter; and (2) a copy of the federal estate tax return.
(C) In addition to the provisions of Section 12-54-70, if the personal representative has obtained an extension of time for filing the federal estate tax return, the filing required by subsection (B) is similarly extended until the end of the time period granted in the extension of time for the federal estate tax return. Upon obtaining an extension of time for filing the federal estate tax return, the personal representative shall provide the department with a copy of the instrument providing for this extension.
(D) Except as provided in Section 12-16-910, the tax due under this chapter must be paid by the personal representative to the Department of Revenue at its office in Columbia not later than the date when the return covering this tax is required to be filed under subsection (B) or (C). If the tax is paid pursuant to subsection (C), interest, at a rate equal to the rate of interest established pursuant to Section 12-54-25, must be added for the period between the date when the tax would have been due had no extension been granted and the date of full payment.