The STC (Secondary Tax on Companies) credit is calculated based on the amount of STC paid by a company on its declared dividends. The credit is calculated as a percentage of the dividends declared and paid by the company. The STC credit is used to offset the company’s income tax liability, thereby reducing the overall tax burden. The specific calculation of the STC credit can vary depending on the company’s financial situation and tax obligations. It is recommended to consult with a tax professional or refer to the relevant tax legislation for accurate guidance on calculating the STC credit. If you have any more questions or need further information, feel free to ask!
The STC credit is comprised of two possible sources:
Any unused STC credits of the company brought forward from the final dividend cycle under the STC system, and
Any new pro rata portion of any STC credit attaching to dividends accruing to the company under the Dividends Tax system. (REF: https://www.sars.gov.za/faq/faq-how-is-the-stc-credit-calculated/)

The STC (Secondary Tax on Companies) credit should be applied by offsetting it against the income tax liability of the company. The credit is typically used to reduce the amount of income tax that the company is required to pay to the South African Revenue Service (SARS). It is important to accurately calculate and apply the STC credit to ensure compliance with tax regulations and to optimize the tax position of the company. If you have any more questions or need further information on applying the STC credit, feel free to ask!
The company paying the dividend must notify the beneficial owner of any part of the dividend that carries a STC credit, and must be applied pro rata to the full dividend. If there is sufficient STC credit to cover the full dividend amount no Dividends Tax becomes payable by the beneficial owner. The remaining STC credit (if any) may be carried forward and be used in respect of future dividends. However, remaining STC credits will expire three years after 1 April 2012. (REF: https://www.sars.gov.za/faq/faq-how-is-the-stc-credit-applied/)

You only have to submit a STC return when it accompanies a STC payment (i.e. when STC is due). This requirement remains the same for the “final dividend cycle” under STC. Where an actual dividend has been declared and the dividend cycle ends on 31 March 2012, a return need only be submitted if STC is due.
Where the dividend cycle is deemed to end on 31 March 2012 (in terms of the proviso to the definition of “dividend cycle” in section 64B(1) of the Act) it is likely that no STC would be payable and hence no return would be required. The use of STC credits under the Dividends Tax system is not linked to the submission (or not) of a STC return. (REF; https://www.sars.gov.za/faq/faq-should-the-company-submit-a-stc-return-it56-reflecting-the-companys-available-stc-credits-for-the-last-dividend-cycle-under-stc-if-it-does-not-will-it-lose-the-stc-credits-under-the-d/)