Provisional tax is not a separate tax. It is the same income tax, paid during the year in instalments rather than in one payment after it.
If you earn income that has no employees' tax deducted from it — which describes almost every business owner and every freelancer — you are almost certainly a provisional taxpayer, whether or not anybody has told you so.
How it works
You estimate what you will earn for the year, and pay tax on that estimate in instalments through the year. At the end, your actual return is assessed and the difference is settled either way.
The mechanism exists because the alternative is a person earning for a full year and then facing a single bill for all of it, which very few people have set aside for.
The estimate is the whole difficulty
Estimate too low and there are penalties for under-estimation, which is the trap for a business that had a strong second half. Estimate too high and you have handed over money you could have used, and you wait for it back.
The practical approach is to base the estimate on what you actually know so far and revise it honestly at the next opportunity rather than repeating the number you first thought of. If the year has gone considerably better than expected, act on that rather than hoping the assessment is forgiving.
Put the money aside as you earn it
This is the entire discipline and it is not complicated: every time money comes in, move a proportion of the profit into a separate account and do not treat it as available.
Businesses that do this find provisional tax an administrative event. Businesses that do not find it a crisis twice a year, and start borrowing to cover it — which is expensive and compounds, because the following year's payments arrive on the same schedule while the debt is still being repaid.
Do not skip a filing because you cannot pay
Filing and paying are separate obligations. A return submitted with a payment arrangement is an entirely different situation from a return not submitted, and the penalties attach differently.
Where you genuinely cannot pay, engage early. Arrangements are possible, and they are considerably easier to obtain from somebody who has filed and asked than from somebody who has gone quiet.
Get help with the first one
A tax practitioner is inexpensive for a small business and this is the area where they earn it fastest — both in getting the estimate right and in making sure you are claiming what you are entitled to. Doing the first year with help and learning the shape of it is a reasonable way to approach it.
General guidance, not tax advice. Deadlines, penalty rules and thresholds change; confirm the current position with SARS or a registered tax practitioner.