A PAYG instalment notice lands every quarter, and most owners glance at the figure, pay it, and move on. Some quarters the number feels wrong. Too high, for a business that has clearly slowed. Suspiciously low, for the quarter trading genuinely took off. Neither reaction is really about this year. The number was never built to reflect this year at all.
The Australian Taxation Office sets most PAYG instalments from your last assessed tax return, adjusted forward by a standard uplift. It is a rearview mirror figure, applied to a business that is, by definition, always looking ahead. For most owner-led businesses along the East Coast, that lag is small enough to ignore. For the businesses genuinely changing pace, accelerating into a strong year or working through a softer one, the gap between what the notice asks for and what the current trading year can actually support becomes a real cash flow event, not just paperwork.
With the September quarter closing and the next instalment due by 28 October, this is the point in the cycle to check that gap before the notice arrives, not after it has already moved money that was earmarked for something else.
How the Instalment Number Actually Gets Set
Most small businesses are placed on the instalment amount method, a dollar figure the ATO calculates from your last lodged return and indexes forward by a standard uplift rate tied to broader economic growth, not your business specifically. Businesses that report GST quarterly can elect the instalment rate method instead, a percentage applied to each quarter’s actual instalment income, which does track the current year more closely because it moves with real revenue as it comes in. Even that rate, though, is set at the point of your last assessment and stays fixed until the next return is lodged. Either method, the anchor point sits months, sometimes well over a year, behind the trading conditions the notice is meant to fund.
This rarely matters for a business holding a steady course. It matters a great deal for a business that has taken on a new contract, lost a major customer, lifted prices meaningfully, or is coming off a one-off strong year that will not repeat. Those are exactly the businesses where the gap between the instalment and the current reality is widest, and exactly the businesses least likely to have budgeted for it either way.
When the Mismatch Cuts Both Ways
When trading has slowed, the instalment amount method keeps asking for a figure sized to a stronger year, pulling cash out of a business that needs it for wages and supplier payments now. The overpayment does come back, but only as a credit at tax time, months after the cash was actually needed, and by then it has already forced a decision about the overdraft or a supplier payment run that a more accurate number would have avoided. When trading has accelerated, the opposite risk shows up. The instalments paid through the year understate the true tax position, and the gap surfaces as a single, larger bill assessed with the annual return, sometimes with a general interest charge attached if the shortfall runs beyond the ATO’s safe harbour margin.
Neither outcome reflects anyone doing anything wrong. It is not a sign your bookkeeper or BAS agent has miscalculated anything, they are applying the ATO’s formula exactly as it is designed to work. It is simply a structural feature of a system built on last year’s numbers, sitting underneath a business that does not stand still.
Before the Next Notice Lands
There is a formal path for correcting the number. A registered agent can lodge a variation when the current year’s income genuinely departs from the assessed baseline, and that conversation is worth having with your accountant well before the due date rather than after the notice has already strained the account. Vary too aggressively without genuine grounds and the ATO can apply penalties if the final figure lands well short, so this is a judgement call made with your compliance accountant, not a form to fill in alone.
The commercial layer that sits alongside that compliance step is different: folding whatever the accurate instalment figure turns out to be into a rolling view of the weeks ahead, so it never arrives as a surprise landing cold in the same fortnight as payroll, superannuation and supplier terms. That is the kind of forward visibility a 13-Week Cash Flow Build is built to provide, and it is one of the more common gaps we see when a fractional CFO reviews a business’s cash rhythm for the first time.
None of this changes what the ATO is owed. It changes whether the payment is a planned line in a forecast or a number that ambushes the account every few months. For owners who want that forward view built properly, our guide to cash flow discipline sets out the rhythm worth building around every recurring obligation, tax instalments included.
Frequently asked questions
What is a PAYG instalment and how is the amount worked out?
A PAYG instalment is a prepayment toward your expected annual income tax, paid quarterly rather than as one lump sum at tax time. The ATO calculates most instalments from your last assessed tax return, indexed forward by a standard uplift rate, rather than from how the current year is actually trading.
Can I vary my PAYG instalment if profit has changed this year?
Yes. A registered tax or BAS agent can lodge a variation when the current year’s income genuinely departs from the figure the instalment was based on. It is worth raising with your accountant ahead of the due date, since the variation adjusts what is paid now rather than waiting for a credit or bill at tax time.
What happens if my business underpays PAYG instalments during the year?
The shortfall is settled when the annual tax return is assessed, as a single larger bill rather than four smaller ones. If the gap runs beyond the ATO’s safe harbour margin, a general interest charge can apply, which is why checking the instalment against actual trading before it compounds matters.
How often are PAYG instalments due for Australian small businesses?
Most businesses pay PAYG instalments quarterly, aligned with the BAS cycle, with the September quarter instalment due by 28 October. Some smaller businesses are eligible to pay annually instead. The due date sits separately from GST and superannuation obligations, even though several land close together.
Is a PAYG instalment the same thing as a BAS payment?
No. A BAS return reports GST, PAYG withholding on wages and other obligations for the quarter just gone. A PAYG instalment is a prepayment toward income tax on the business’s own profit for the year ahead. They are often paid at the same time, which is part of why the timing feels heavier than either bill alone.
Why does my PAYG instalment feel too high when trading has slowed?
Because the standard instalment amount method is set from your last assessed return, not the current quarter’s results. If this year is genuinely softer than last year, the instalment can keep asking for cash sized to a stronger period until a variation is lodged or the year is reassessed.
How does a fractional CFO help with tax instalment cash flow planning?
A fractional CFO does not replace the work of your tax agent, who calculates and lodges the correct figure. The role is building the rolling cash flow view that places each instalment, whatever the confirmed number is, alongside payroll, super and supplier payments, so the timing never catches the business by surprise.
Leave a Reply