Provisional tax is not a separate tax but rather a method of payment used to collect in advance some of a taxpayer’s income tax payable for the year. SARS calls it “an advance payment of a taxpayer’s normal tax liability” and notes in its External Guide for Provisional Tax that provisional tax liability “will prevent a large amount of tax due by you on assessment, as your tax liability will have been spread over a period of time
prior to the issue of such assessment”.

Two provisional tax payments are compulsory each year, one six months into the year of assessment (first period) and one on or before the end of the year of assessment (second period). There is also an option to make an additional third or top-up payment, seven months after the end of the year of assessment – unless your year end is anything other than end of February in which event you have only six months for the top-up
payment (third period).

Read more here