BAS Calculator Australia

What Is a BAS?

A Business Activity Statement is how most GST-registered Australian businesses report GST (and often PAYG instalments, PAYG withholding and other obligations) to the ATO. You do not invent the form — the ATO issues your BAS with the labels that apply to you.

For GST, the number that decides whether you pay or get a refund is simple in structure: GST on sales minus GST credits on purchases. The messy part is classification — what sits in taxable sales, what is GST-free, and which purchases are actually creditable.

Official overview: ATO business activity statements.

How Is BAS Calculated?

For a typical small business on Simpler BAS, the GST path looks like this for each tax period:

1. Add total sales for the period (that becomes G1, including GST where charged).
2. Calculate GST on taxable sales only → label 1A.
3. Calculate GST credits on eligible purchases → label 1B.
4. Net GST = 1A − 1B. Positive means you generally pay; negative means a credit/refund position.
5. If you have PAYG instalments, calculate that amount separately — do not fold it into 1A/1B.

Full reporters also split sales into exports (G2) and other GST-free sales (G3), and purchases into capital (G10) and non-capital (G11). The GST maths for 1A and 1B still drives the net GST figure.

How to Calculate GST for BAS

Australia’s GST rate on taxable supplies is 10% (unchanged since 1 July 2000). Use one of these:

• GST-inclusive price: GST = amount ÷ 11
• GST-exclusive price: GST = amount × 10%

Example: $11,000 including GST contains $1,000 GST ($11,000 ÷ 11). The same sale exclusive of GST would be $10,000, and GST is $1,000 ($10,000 × 0.10).

Not every dollar of sales creates GST. Exports, many basic foods, some education and health supplies, and input-taxed supplies (like much residential rent) sit outside taxable GST — but they can still affect G1 or other labels depending on the reporting method.

BAS Calculation Formula

For GST:

Taxable sales → GST collected (1A)
Eligible purchases → GST credits (1B)
Net GST = 1A − 1B

Worked sole-trader style example (GST-inclusive figures, Simpler BAS): taxable sales $55,000, other GST-free sales $5,000, non-capital purchases $11,000.

That $5,000 GST-free sales lifts G1 but does not increase 1A. If your purchases were not creditable, 1B would be $0 and you would pay the full 1A.

What Is G1 on a BAS?

G1 is total sales for the reporting period. On Simpler BAS it is one of only three GST labels you report. It is not “taxable sales only” — GST-free and other sales that belong in total sales still go here under ATO instructions.

Getting G1 wrong is common when people paste bank deposits without separating owner drawings, loans, or sales that belong in a different period.

What Are 1A and 1B?

1A — GST on sales is the GST attributable to taxable supplies in the period. 1B — GST on purchases is the GST credits you can claim on eligible acquisitions.

Net GST payable or refundable for the period is 1A minus 1B. The calculator on this page shows that difference as the headline result and lists the labels in a worksheet table.

Simpler BAS vs Full BAS

Simpler BAS is the default for eligible small businesses with GST turnover under $10,000,000. You report G1, 1A and 1B for GST on the activity statement.

Full reporting generally applies when GST turnover is $10,000,000 or more. You also report G2 (exports), G3 (other GST-free sales), G10 (capital purchases) and G11 (non-capital purchases).

Some businesses below the $10 million threshold may still use or elect full reporting depending on circumstances — check ATO GST reporting methods and Simpler BAS bookkeeping guidance.

GST-Free vs GST-Applicable Sales

Taxable sales attract 10% GST. GST-free sales (for example many basic foods, exports, some education and health supplies) do not. Input-taxed sales (for example much residential rent and some financial supplies) also do not charge GST — and you generally cannot claim credits that relate to making those supplies.

Do not assume a sale is taxable because money hit your account. Classify from the supply type, then calculate GST only on the taxable portion.

GST Credits on Purchases

Credits usually require that you are GST-registered, the purchase is for a creditable purpose, and you hold a valid tax invoice when the amount requires one. Purchases from businesses that are not GST-registered typically contain no GST to claim.

Capital purchases (equipment, vehicles used in the business) and day-to-day non-capital purchases both feed 1B when eligible. Full reporters also show them at G10 and G11. Private use reduces the creditable amount — the worksheet lets you strip a private portion before GST is calculated.

GST Registration Threshold

Most businesses must register for GST once annual GST turnover reaches $75,000. Not-for-profits generally sit at $150,000. Taxi and ride-sourcing operators have special rules and usually must register regardless of turnover.

You can register voluntarily below the threshold. Once registered, you charge GST on taxable sales and lodge BAS according to your cycle.

BAS for Sole Traders

Sole traders use the same GST labels. The trap is mixing personal spending with business purchases. If half a phone bill is private, only the business portion is generally creditable. Quarterly lodgers often underestimate how much “messy” banking costs them at BAS time — clean categories beat a clever calculator.

If your taxable sales are modest and purchases are heavy in a fit-out quarter, 1B can exceed 1A and you land in a refund position. That is normal; it is not a sign the calculator is broken.

BAS for Small Businesses

Most small GST-registered businesses lodge quarterly. Monthly GST reporting is generally required when GST turnover reaches $20,000,000, or if you choose monthly. Accounting software often pre-fills labels from coded invoices — you still need to check GST codes before lodgment.

PAYG Instalments on a BAS

PAYG income tax instalments can appear on the same BAS as GST. They are not GST. The ATO may notify an instalment amount (sometimes adjusted by a GDP factor) or an instalment rate applied to instalment income.

For 2026–27, the ATO GDP adjustment factor for applicable instalments is 5%. The calculator’s PAYG section can apply that factor to a notified amount, or estimate instalment × rate — shown separately from net GST so you do not confuse the two.

BAS Calculation Worksheet

Keyword research around “BAS calculation sheet” and “BAS calculation spreadsheet” points to one need: a transparent working paper. The interactive worksheet at the top of this page fills that role — enter sales and purchases, switch Simpler vs Full, override 1A/1B if your ledger already shows GST, copy the label summary, and reset when you start a new period.

It does not file your BAS. Lodgment still happens in ATO online services, Online services for agents, or your approved software.

Common Mistakes

• Treating all bank deposits as taxable sales
• Claiming GST credits without a tax invoice when one is required
• Applying ÷11 to GST-free amounts
• Mixing PAYG instalments into the GST payable figure
• Using Simpler BAS labels when you are required to report in full
• Forgetting private-use adjustments on mixed purchases