# BAS calculator (GST payable)

Source: https://calculatax.com/gst/bas-calculator/
Title: BAS Calculator: Work Out GST Payable or Refund | Calculatax
Last updated: 2026-11-07

This BAS calculator turns a period's sales and purchases into GST on sales (label 1A), GST credits (label 1B) and the net GST payable or refundable. It uses the ATO's 10% rate for 2026-27. A quarter with $44,000 of sales ($4,000 of them GST-free) and $13,200 of purchases gives **$2,436.36** payable.

It handles the GST section of a Business Activity Statement (BAS) only. Registration rules and how the tax works sit under [GST in Australia](https://calculatax.com/gst/), and the [GST calculator](https://calculatax.com/gst/gst-calculator/) checks a single price.

| Default example: BAS item | Label | Default quarter |
|---|---|---|
| Total sales, including GST | G1 | $44,000.00 |
| GST-free sales included in G1 | G3 | $4,000.00 |
| Taxable sales, including GST | Working | $40,000.00 |
| GST on sales ($40,000 ÷ 11) | 1A | $3,636.36 |
| Purchases, including GST | Working | $13,200.00 |
| GST credits ($13,200 ÷ 11) | 1B | $1,200.00 |
| Net GST payable (1A minus 1B) | Result | $2,436.36 |
| Net GST on the form, whole dollars | Result | $2,436 |

*Default quarter at the 10% GST rate, 2026-27. Source: ATO rate; Calculatax calculation.*

## Labels G1, 1A and 1B in plain English

Three labels do most of the work, and the difference between the last two is what you pay or get back.

1. **G1 is your total sales.** Every sale in the period goes here, GST-free sales too.
2. **1A is the GST you collected.** Only taxable sales count. Take out the GST-free sales, then divide by 11.
3. **1B is the GST you can claim.** That's the GST in purchases you use in the business, also divided by 11.

> **Don't divide all of G1 by 11 if some sales are GST-free.** On the $44,000 quarter that gives $4,000 at 1A, which overstates the GST by $363.64.

### More on G1 and the other sales labels

The form asks whether your G1 figure includes GST, so answer that to match your records. This calculator takes G1 with GST included.

Full reporting also splits out export sales at G2 and other GST-free sales at G3. On Simpler BAS you report only G1, 1A and 1B.

Input-taxed sales go in G1 as well, and they carry no GST. Add them to the GST-free field so they stay out of 1A.

Credits can pass the GST on your sales, and then the ATO owes you the difference. Say that same business also bought a $55,000 excavator, including GST, in that quarter.

**A quarter that ends in a refund**

| Step | Working | Amount |
|---|---|---|
| GST on sales | $40,000 ÷ 11 | +$3,636.36 |
| GST on everyday purchases | $13,200 ÷ 11 | -$1,200.00 |
| GST on the excavator | $55,000 ÷ 11 | -$5,000.00 |
| **GST refund** |  | **$2,563.64** |

*2026-27, at the 10% GST rate. Source: ATO rate; Calculatax calculation.*

The ATO's [instructions for completing your BAS](https://www.ato.gov.au/businesses-and-organisations/gst-excise-and-indirect-taxes/gst/completing-your-bas-for-gst/complete-your-bas) ask you to round down to whole dollars, with no cents. So $3,636.36 at 1A goes on the form as $3,636. The calculator shows the cents as well, so you can match it to your accounts.

## Cash or accrual reporting

Your accounting method decides which period a sale or purchase lands in. The ATO calls accrual the non-cash basis.

| Same invoice, two methods | Cash basis | Non-cash (accrual) basis |
|---|---|---|
| When GST counts | The period you receive or make payment | The period an invoice is issued or received, or a payment happens if that's earlier |
| $5,500 sale invoiced 20 June, paid 10 July: $500 of GST | July to September quarter | April to June quarter |
| $1,100 bill dated 25 September, paid 3 October: $100 credit | October to December quarter | July to September quarter |

*You need a tax invoice before you can claim the credit on that bill. Source: ATO.*

Businesses with aggregated turnover below $10 million can choose either method, as the ATO's page on [choosing an accounting method for GST](https://www.ato.gov.au/businesses-and-organisations/gst-excise-and-indirect-taxes/gst/accounting-for-gst-in-your-business/choosing-an-accounting-method) explains. The ATO says the cash basis lines up your BAS with the money moving through the business, while the non-cash basis suits businesses that aren't paid straight away. Enter sales and purchases here on the same basis your business uses.

## Quarterly BAS due dates

You lodge quarterly if your GST turnover is under $20 million and the ATO hasn't told you to report monthly. The GST and any other amounts on the form are paid by the same date.

| Quarter | Months covered | Due date |
|---|---|---|
| Quarter 1 | July to September | 28 October 2026 |
| Quarter 2 | October to December | 28 February 2027 (a Sunday, so Monday 1 March 2027) |
| Quarter 3 | January to March | 28 April 2027 |
| Quarter 4 | April to June | 28 July 2027 |

*Quarterly BAS dates for 2026-27. A due date on a weekend or public holiday moves to the next business day. Source: [ATO due dates for lodging and paying your BAS](https://www.ato.gov.au/businesses-and-organisations/preparing-lodging-and-paying/business-activity-statements-bas/due-dates-for-lodging-and-paying-your-bas).*

### Extra time, monthly and annual reporting

Lodging online may give you an extra 2 weeks for a quarterly BAS. That doesn't apply to quarter 2, whose date already includes a one-month extension. Lodging through a registered tax or BAS agent can also give you more time.

With GST turnover of $20 million or more you must report monthly, by the 21st of the following month.

If you registered voluntarily and your GST turnover is under $75,000, you lodge once a year.

## GST-free sales and purchases you cannot claim

GST-free sales go into G1 but add nothing to 1A. Common examples are basic food, most health services and exports.

A credit only exists for GST included in the price of something you use in the business. You can't claim at 1B for:

- GST-free purchases, because they contain no GST.
- Input-taxed purchases, such as bank fees and loan interest. Wages carry no GST either.
- The private-use share of a purchase.
- Purchases from suppliers who aren't registered for GST, because no GST is in the price.
- Purchases over $82.50 including GST, until you hold a tax invoice, as the ATO's page on [when you can claim a GST credit](https://www.ato.gov.au/businesses-and-organisations/gst-excise-and-indirect-taxes/gst/claiming-gst-credits/when-you-can-claim-a-gst-credit) explains.

Private use changes the answer quickly. If $2,200 of the $13,200 in purchases was private, only $11,000 is claimable, so 1B falls to $1,000.00 and the net GST rises to $2,636.36.

## When your BAS figure will differ

This works out the GST section only. A full BAS can also carry PAYG instalments, fuel tax credits and the tax you withhold from wages, which the [PAYG withholding calculator](https://calculatax.com/tax/payg-withholding-calculator/) estimates. Those amounts change what you pay.

It also treats every taxable sale and purchase as 10%, and you decide which sales are GST-free. It doesn't handle GST adjustments, reverse charges, imports or special property rules. If any of those apply, a registered BAS agent or tax agent can prepare the statement.

### Nil periods and fixing mistakes

If you're registered for GST and have nothing to report, you still lodge your BAS as nil by the due date.

Mistakes on an earlier BAS can often be fixed on a later one, within the limits in the ATO's [types of GST errors](https://www.ato.gov.au/businesses-and-organisations/gst-excise-and-indirect-taxes/gst/completing-your-bas-for-gst/correcting-gst-errors/types-of-gst-errors) page. With GST turnover under $20 million, net debit errors under $12,500 can go on a BAS lodged within 18 months of the original due date.

Credit errors have no value limit, but you fix them within the period of review, which runs 4 years and one day from when you lodged. GST credits have their own 4-year time limit too.

## BAS questions: sole traders, GST payable, credits and paying

### Do I need to lodge a BAS as a sole trader?

Yes, if you're registered for GST. You must register once GST turnover reaches $75,000, or at any turnover for taxi and ride-sourcing work. If you aren't registered you don't report GST, though the ATO may send you an instalment notice for PAYG instalments.

### How do you calculate GST payable?

It's the GST on your sales at 1A minus your GST credits at 1B. On $40,000 of taxable sales including GST, 1A is $3,636.36. With $13,200 of purchases including GST, 1B is $1,200.00, so $2,436.36 is payable. If 1B is larger than 1A, the ATO refunds the difference.

### How is a GST credit calculated?

Divide the GST-inclusive price of a purchase by 11, then keep only the business share. Purchases of $13,200 including GST give a $1,200.00 credit, and $11,000 of them gives $1,000.00. Input-taxed purchases and GST-free purchases give no credit.

### How do you pay a BAS?

You pay the ATO by the due date and quote your payment reference number (PRN). The ATO calls BPAY or its online services the quickest way to pay. Direct debit, EFT and Australia Post also work. You can't use a credit card to pay the ATO after 30 June 2027.

*Estimates only, based on published rates for 2026-27. General information, not tax or financial advice.*

## Sources

- [ATO: Instructions for completing your BAS](https://www.ato.gov.au/businesses-and-organisations/gst-excise-and-indirect-taxes/gst/completing-your-bas-for-gst/complete-your-bas)
- [ATO: Due dates for lodging and paying your BAS](https://www.ato.gov.au/businesses-and-organisations/preparing-lodging-and-paying/business-activity-statements-bas/due-dates-for-lodging-and-paying-your-bas)
- [ATO: Choosing an accounting method for GST](https://www.ato.gov.au/businesses-and-organisations/gst-excise-and-indirect-taxes/gst/accounting-for-gst-in-your-business/choosing-an-accounting-method)
- [ATO: When you can claim a GST credit](https://www.ato.gov.au/businesses-and-organisations/gst-excise-and-indirect-taxes/gst/claiming-gst-credits/when-you-can-claim-a-gst-credit)
- [ATO: Types of GST errors](https://www.ato.gov.au/businesses-and-organisations/gst-excise-and-indirect-taxes/gst/completing-your-bas-for-gst/correcting-gst-errors/types-of-gst-errors)