If FY26 was a good year for your business, first, well done. Revenue is up, margins held, and you’re finally starting to feel like the business works for you instead of the other way around.
Now here’s the less exciting part: your tax bill grew too. And if your February 2026 year-end business paid its second provisional tax estimate back in August based on numbers that didn’t quite keep up with how well you actually did, SARS is already running the interest clock on the shortfall, quietly, in the background, whether you’ve noticed it or not.
The good news is you still have a window to close that gap on your own terms. It’s called the voluntary third top-up payment, and for Feb year-end taxpayers, it’s due by 30 September 2026.
This isn’t a penalty notice. It’s a discipline move, one more sign that you’re running your business like an owner who plans ahead, not one who gets surprised by their own success.
Who This Actually Applies To
This one is specific, so let’s be precise about it.
This applies to you if:
- Your company or you (as a provisional taxpayer) has a February year-end
- You submitted your second provisional tax payment in August 2026, based on an estimate of taxable income for the full year
- That estimate turned out to be lower than what your actual results now show, because trading was stronger in the second half of the year than you projected, a big project landed, or you were simply conservative when you filed
If any of that describes you, you’re not in trouble. You’re in the position most growing businesses eventually find themselves in: last year’s estimate didn’t keep pace with this year’s growth. That’s a good problem.
This is different from the mandatory second provisional payment deadline in August, which every provisional taxpayer with a February year-end has to meet regardless of how accurate their estimate is. We’ve covered that deadline in detail elsewhere on the site. The third top-up is a completely separate, voluntary mechanism that exists specifically to let you correct an underestimation before SARS calculates it for you, with interest attached.
The Interest Math: Pay Now vs. Wait for Assessment
Here’s the part most business owners skip past, and it’s the part that actually matters.
If your second provisional payment underestimated your actual taxable income, SARS doesn’t wait for your annual assessment to notice. Once your return is assessed and the shortfall is confirmed, interest accrues from the effective date of the second provisional payment, not from assessment date, not from today. That interest has been ticking since August, and it keeps ticking until you settle it, whether that’s now or eight months from now when your assessment finally comes through.
A voluntary top-up paid by 30 September doesn’t erase that interest entirely, some may still apply for the period between August and now, but it stops the clock immediately instead of letting it run for months while your return sits in a queue. The longer you wait, the bigger the number, and it compounds on a balance you already know exists.
Put simply: this is a bill you’re going to pay one way or another. The only real decision is whether you pay it now, on a number you calculate yourself with full visibility, or later, on a number SARS calculates for you with several extra months of interest baked in.
For a business that had a genuinely strong year, that interest is real money walking out the door for no reason other than timing. It’s the kind of leak that’s easy to miss when you’re focused on delivery, clients, and growth, and exactly the kind of thing a proper finance function should be catching before it becomes a surprise.
Growth Doesn’t Just Grow Your Revenue, It Grows Your Tax Bill
Here’s the mindset shift worth sitting with: as your consultancy, agency, or firm scales, your tax position scales with it. That’s not a downside of growth, it’s a sign it’s working. But it does mean the estimates and assumptions that worked when you were smaller need to be revisited more often, not left on autopilot.
Businesses that are used to being “too small for a full-time CFO” often don’t have anyone whose job it is to notice mid-year that actual performance has outpaced the tax estimate filed months earlier. It’s nobody’s fault, it’s just a gap that opens up naturally when finance is something you get to between everything else.
The businesses that come out ahead here aren’t the ones who guessed better. They’re the ones who checked in on their numbers before the deadline, rather than after the assessment. That’s the whole game with provisional tax: it rewards businesses that treat their financials as something to actively manage, not just report on once a year.
If FY26 outperformed your own expectations, that’s exactly the moment to get a proper read on where your tax position actually stands, not after SARS tells you.
Get Ahead of It Before 30 September
If you had a strong FY26 and you’re not sure whether your August provisional estimate is still accurate, don’t wait for your assessment to find out. A quick recalculation now could save you months of accumulating interest, and give you a much clearer picture of where your business actually stands heading into the new financial year.
Grab our Easy Profitability Toolkit for a practical way to check your numbers and stay ahead of moments like this one, or skip straight to talking it through with someone who deals with this every day.
Book a call with the ThriveCFO team before 30 September, and let’s make sure your good year stays a good year, interest-free.
