The deadline to file your South Carolina return is April 18th, 2022 unless you have a valid extension.
According to the South Carolina DOR:
"If you file using a calendar year end of December 31, your Estimated Tax payments are due in four equal installments:
• 1st quarter due April 15, 2021
• 2nd quarter due June 15, 2021
• 3rd quarter due September 15, 2021
• 4th quarter due January 18, 2022
You can choose to pay all of your Estimated Tax on April 15, the due date of the first installment. Instead of making your last payment
on January 18, you can choose to file your SC1040 by February 1 and pay the full balance of Income Tax due.
If you are not required to file on April 15 and:
• you meet your Estimated Tax filing requirement after April 1 and before June 1, your first Estimated Tax payment is due on
June 15, 2021.
• you meet your Estimated Tax filing requirement after June 1 and before September 1, your first Estimated Tax payment is
due on September 15, 2021.
• you meet your Estimated Tax filing requirement after September 1, your first Estimated Tax payment is due on January 18,
2022.
3. If you file on a fiscal tax year, your Estimated Tax payments are due on the 15th day of the fourth, sixth, and ninth months of the
fiscal year and the first month of the following fiscal year. "