BAS Calculator 2026-27

Work the three sections separately, then subtract once. Nothing on a BAS mixes GST with withholding until the summary block on the back of the form.

1. GST. Take your total sales at G1, strip out the export, GST-free and input taxed sales, add any increasing adjustments, and divide by 11. That is 1A. Do the same on the purchases side and that is 1B. Net GST is 1A minus 1B.
2. PAYG withholding. Report the gross payments at W1 and the tax you took out at W2. Add W2, W4 and W3 to get W5, and copy W5 to label 4. W1 never enters the total.
3. PAYG instalment. Either take the amount the ATO printed at T7, or multiply your instalment income at T1 by the rate at T2 to get T11. Whichever you use goes to 5A.
4. Summary. 8A is everything you owe: 1A plus label 4 plus 5A. 8B is everything the ATO owes you: 1B plus any credit at 5B. Label 9 is 8A minus 8B. Positive means you pay, negative means a refund.

Every label goes on in whole dollars with the cents dropped. The ATO wording is "round down to whole dollars" and "leave cents out and don't round up to the next dollar", and its own worked example reports $341.70 as 341. The calculator applies that rule at each label, which is why a figure here can sit a dollar below what a spreadsheet gives you.

If your statement only carries PAYG obligations and no GST, you are lodging an instalment activity statement rather than a BAS. The withholding and instalment halves of this page still apply, and the instalment activity statement guide covers who gets one.

The labels below are the ones this calculator models. A statement can also carry wine equalisation tax at 1C and 1D, luxury car tax at 1E and 1F, fringe benefits tax instalments at 6A and 6B, and fuel tax credits at 7C and 7D. Those are not modelled here.

GST is 10% for 2026-27 on most goods, services and other items sold or consumed in Australia. On the activity statement it occupies three labels under Simpler BAS: G1 for total sales, 1A for the GST you collected, and 1B for the GST you paid and can claim back. The ATO states the rate without a year table, so there is no separate 2026-27 figure to look up.

Divide by 11, not multiply by 10%

This is where most manual BAS errors start. If a sale was $1,100 including GST, the GST is not $110 taken as 10% of $1,100. It is $100, because a GST-inclusive price is 110% of the GST-exclusive price, so the GST part is 10 of those 110, which is one eleventh. The ATO worksheet gives the instruction directly: at G9, divide G8 by 11 and transfer the answer to 1A, and at G20, divide G19 by 11 and transfer the answer to 1B.

What comes out before the divide

Only taxable sales carry GST, so three categories come out of G1 first. G2 is your export sales, G3 is other GST-free sales such as basic food and most health and education services, and G4 is input taxed sales such as residential rent and financial supplies. G4 is worth watching: it never appears on the statement, but leaving it in inflates 1A. The same logic applies on the purchases side, where G13, G14 and G15 take out the purchases you cannot claim a credit on.

You only reach these labels if you are registered

GST registration is compulsory once your GST turnover reaches $75,000, or $150,000 for a non-profit organisation, and you have 21 days to register from the point you cross it. Taxi, limousine and ride-sourcing drivers register regardless of turnover. The two-limb test looks at your current turnover, being this month plus the previous 11, and your projected turnover, being this month plus the next 11. Our sole trader tax calculator and the ABN tax guide both cover what registration changes about your income tax, and the contractor pay calculator shows what a GST-inclusive day rate is actually worth once the ATO takes its eleventh.

Your GST turnover decides how many labels you fill in. Under $10 million you are on Simpler BAS by default and report three GST labels. At $10 million or more you must use the full reporting method, which adds four more. Simpler BAS has been the default for small business since the 2017-18 year, and the ATO rolls your method over each financial year based on the turnover it holds for you.

Simpler BAS drops the GST calculation worksheet, not your record keeping. You still need a valid tax invoice for any purchase of $82.50 including GST or more before you claim the credit, you still classify each sale correctly behind the scenes, and you still keep the records for five years. The calculator above defaults to Simpler BAS and hands you the worksheet anyway, because the worksheet is how you get to 1A and 1B in the first place.

Two options sit outside the turnover test. If your aggregated turnover is above $10 million, or your main business activity is making input taxed supplies, you may choose either method. And if you are voluntarily registered below $75,000, you can elect to report and pay annually instead of quarterly.

If you pay anyone, this section is usually the biggest number on the statement. W1 is the gross total of payments you normally withhold from. W2 is the tax you took out of them. You pay W2, and W1 is reported for the ATO to reconcile against.

The list of what belongs at W1 is longer than most people expect: salary, wages, allowances and leave loading, director fees, salary and allowances paid to office holders, payments to labour hire workers, employment termination payments, payments for unused annual or long service leave, payments to religious practitioners, super income streams and lump sums, Commonwealth education and training payments, and attributed personal services income. Salary sacrificed amounts and super contributions stay out.

Add W2, W4 and W3 to get W5, then copy W5 to label 4 in the summary. W1 stays out of that total. Two special cases change the section entirely. Report through Single Touch Payroll and you no longer report W1 on your activity statements at all. And a large withholder, meaning one that has withheld more than $1 million in a previous income year, completes only W1 and pays electronically instead.

To check the W2 figure itself, work each employee through the PAYG withholding calculator and add the results. The PAYG withholding guide covers registration, the scales and what happens when you get it wrong.

A PAYG instalment is a prepayment of the income tax on your business and investment income. It has nothing to do with GST and nothing to do with what you withheld from staff. The ATO gives you two options on your first statement of the income year.

Option 1 pays the amount the ATO worked out. It is printed at T7, and you copy it to 5A. If you think it is wrong for the year ahead you can vary it, entering your estimated tax for the year at T8, the varied amount at T9 and a reason code at T4. Varying does not change what you owe for the year, only the timing.

Option 2 multiplies income by a rate. Enter your instalment income at T1, take the rate the ATO printed at T2, and T11 is T1 multiplied by T2. That goes to 5A. Instalment income is gross business and investment income excluding GST, which trips people up: a $22,000 sale that included $2,000 of GST contributes $20,000.

That example is the ATO's, published in its instructions for completing the instalment section, and it is the anchor case in this site's engine tests. Note the rounding: $341.70 becomes $341, not $342.

If you varied down earlier in the year you may be able to claim a credit at 5B for the instalments you already paid at the higher figure. The ATO publishes a seven-step table for working that credit out, and you can also skip it and let the credit fall out when you lodge your tax return. The PAYG instalment calculator works out the instalment itself, the PAYG instalments guide covers who gets put into the system and how to get out, and varying your PAYG instalments covers T8, T9 and the reason codes.

Six quarters, each computed by the same engine that runs the calculator above. Watch how the GST half stays constant across examples 1 to 3 while the payment goes from $6,000 to $20,000, because wages and instalments are added on top of the GST rather than mixed into it.

Example 5 is the case that catches new food businesses. Sales of $110,000 look like $10,000 of GST, but $77,000 of it was GST-free basic food, so only $33,000 is taxable and 1A lands at $3,000. With $2,000 of credits the statement comes to $1,000. Miss the G3 step and you overpay by $7,000 for the quarter.

Your cycle follows your GST turnover. Under $20 million you report quarterly unless the ATO has told you otherwise. At $20 million or more you report monthly, due the 21st of the following month. If you are voluntarily registered under $75,000 you can elect to report annually, due 31 October, or 28 February following the annual tax period if you are not required to lodge a tax return then.

The quarter end dates and the 28th-of-the-month pattern come from the ATO. Applying them to the 2026-27 calendar is our arithmetic, and so is the shift on quarter 2, which uses the ATO rule that a due date falling on a weekend or public holiday moves to the next business day. Public holidays are not modelled here, so a state holiday could move a date again. Lodging online can add two weeks on quarters 1, 3 and 4, and a registered agent may get you more, but quarter 2 gets nothing further because its date already carries a one-month extension. Every PAYG deadline for the year sits in the PAYG due dates guide.

Most GST mistakes can be fixed in your current statement. Clerical errors and double-counted purchases qualify, and so do adjustments where a price changed or goods were returned and the sale was cancelled. Where the correction is too large for the current statement, revise the original one. The same record-keeping habit that fixes this also fixes the withholding side, which is covered in PAYG in Xero and MYOB.