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