The maximum for 2017 was $210 (0.7% of $30,000), but the cap is increasing gradually until it reaches $350 (0.7% of $50,000) for 2023. So the max credit for tax year 2020 will be $280, for 2021 it will be $303, and for 2022 it will be $327. The calculation is right, the worksheet is wrong,
https://law.justia.com/codes/south-carolina/2018/title-12/chapter-6/section-12-6-3330/
