The Payment Nobody Is Forced to Make
Provisional taxpayers know the two compulsory dates: end of August and end of February. There's a third date that appears on no demand and arrives with no penalty attached — and for taxpayers who had a strong year, it's the cheapest money-saving move available this month.
The voluntary third payment (often called the "top-up" or additional payment) lets you settle any remaining 2025/26 shortfall by 30 September 2026 — seven months after the February year-end. Its entire purpose is interest: get the year fully paid by that date, and section 89quat interest never starts running against you.
How the Interest Works
When your ITR12 for 2025/26 is eventually assessed, SARS compares your final liability with what you actually paid through provisional payments and PAYE. If you underpaid, interest at the prescribed rate runs on the shortfall from the effective date — 30 September 2026 — until the date of assessment.
Note what that means about timing:
- The interest clock doesn't start when you file, or when SARS assesses. It runs retrospectively from 30 September. File your return in January 2027 with a R60,000 shortfall, and the assessment arrives with months of interest already attached.
- Conversely, a top-up that lands by 30 September means there is no shortfall for the clock to run on.
The prescribed rate is meaningfully higher than what your money earns in a savings account, which settles the "should I hold onto the cash instead" question for most people: if you know you owe it, paying by the effective date is the better trade.
Who Should Be Doing This Calculation
The top-up matters when your February estimate turned out low. Common versions:
- The year finished stronger than the February estimate assumed. A late-February invoice run, a project that closed bigger than projected.
- You used the basic amount through the year while income grew. The gap between the basic amount and reality is now a shortfall accruing toward interest.
- A capital gain landed late in the year — a property or share disposal in December–February that the estimates never captured.
- Deductions came in lower than planned — the RA contribution you budgeted for but didn't make, for example.
If, on the other hand, your February estimate was accurate or generous, there's nothing to do — and if you overpaid, your money comes back with the assessment (and in some circumstances SARS pays interest on genuine overpayments above a threshold).
The 30-Minute Calculation
You're now seven months past year-end; the numbers are no longer estimates.
- Final income for 2025/26 — actual invoiced-and-received business income for March 2025 to February 2026, plus interest, rental, and any capital gains.
- Final deductions — actual business expenses, home office, travel per the closed logbook, s11F retirement contributions per your certificates.
- Tax on the result — apply the 2025/26 table and rebates.
- Less what you've paid — both IRP6 payments and any PAYE withheld.
A positive difference is your shortfall. Two rules of thumb from there: if it's trivial, ignore it — the interest on a small shortfall is noise. If it's five figures, the top-up almost certainly beats holding the cash.
Making the Payment
The top-up is made as an additional provisional payment for the 2026 period on eFiling — request the IRP6 for the third period (period 3) against the 2025/26 year, capture the amount, and pay with the reference the form generates. The mechanics matter: a top-up allocated to the wrong period or paid on a generic reference can sit unmatched, defeating the purpose. Confirm on your statement of account that the payment reflects against the 2026 year of assessment.
Then file the ITR12 itself without unnecessary delay. The top-up stops interest; filing crystallises the refund or the (now settled) liability, and your assessed figure becomes the basic amount that anchors next year's estimates.
The Larger Pattern
The third payment rewards exactly one behaviour: knowing your actual numbers shortly after year-end instead of at filing time. Freelancers who reconcile their year in March know by April whether a top-up will be needed and can plan the cash. Those who first look in January discover the shortfall and the interest together.
Wherever you are on that spectrum this September — run the calculation before the 30th. It's half an hour that either confirms you're clean or saves you months of interest at the prescribed rate.