GST Calculator

How Goods and Services Tax (GST) works

Goods and Services Tax (GST) is a multi-stage, destination-based consumption tax levied on the sale of goods and services. Whether you are invoicing clients, preparing retail receipts, or managing cross-border transactions, determining the correct tax component is essential for tax compliance and cash-flow management. All calculations run directly in your browser without transmitting sensitive financial data to an external server.

This calculator supports both forward calculations (adding GST to a net base price) and reverse calculations (extracting the tax embedded in a gross price). If you offer retail markdowns before tax is assessed, you can first verify net sale prices using our discount calculator. If you are pricing goods or invoicing clients in Quebec, calculate the combined provincial and federal taxes using our GST QST calculator. For business owners balancing payroll deductions against sales tax obligations, our gross pay calculator helps project direct wage costs, while self-employed contractors can evaluate their federal obligations with the 1099 tax calculator.

GST mathematical formulas

Depending on whether a price quote is tax-exclusive or tax-inclusive, you will apply either the forward addition formula or the reverse extraction formula.

1. Adding GST to a net price (tax-exclusive)

When you know the base price of a product or service and need to add GST, multiply the net amount by the decimal tax rate:

Here, $r$ denotes the statutory percentage tax rate. For example, on a $500 invoice subject to Australia's 10% GST, the tax is $500 \times 0.10 = \$50$, resulting in a gross invoice of $550.

2. Extracting GST from a gross price (tax-inclusive)

In many consumer retail environments, displayed shelf prices already include GST. Because the tax was applied to the net base rather than the final total, you cannot simply multiply the gross total by the tax rate. Doing so would overstate the tax liability. Instead, divide by one plus the tax rate:

This relationship yields standard statutory shortcuts:

• 10% GST (Australia): Dividing by $1 + 0.10$ simplifies to extracting GST by dividing the gross price by 11 ($10 / 110 = 1 / 11$).
• 15% GST (New Zealand): Multiplying by $15 / 115$ simplifies to multiplying the gross total by the fraction 3/23.
• 9% GST (Singapore): The tax extraction fraction is $9 / 109$.

International GST rate benchmarks (2025/2026)

Different jurisdictions implement GST with varying standard rates, zero-rated exemptions, and sub-national mechanisms. The table below outlines standard GST schedules across major international systems:

Step-by-step worked examples

Worked example 1: Calculating invoice GST in Australia (10%)

A supplier provides consulting services billed at a pre-tax base rate of $1,200. With Australia's 10% GST:

1. Multiply the net base by 10%: $1200 \times 0.10 = \$120.00$.
2. Add tax to the net price: $1200 + 120 = \$1,320.00$.
3. The tax invoice displays a net fee of $1,200, GST of $120, and a total payable of $1,320.

Worked example 2: Extracting GST from a tax-inclusive retail receipt in New Zealand (15%)

A retail customer buys electronic goods for an all-inclusive receipt total of $230 in Auckland, New Zealand:

1. Divide total by 1.15: $230 / 1.15 = \$200.00$ net amount.
2. Extract the embedded GST: $230 - 200 = \$30.00$ (or $230 \times (3 / 23) = \$30.00$).
3. The merchant remits $30 in GST and retains $200 in net revenue.

Worked example 3: India intra-state supply (18% GST)

A software company in Karnataka sells a software license to a local business for $1,000 net:

1. Calculate total GST at 18%: $1000 \times 0.18 = \$180.00$.
2. Split the tax evenly between Central and State authorities: CGST (9%) is $90.00 and SGST (9%) is $90.00.
3. The final bill total is $1000 + 180 = \$1,180.00$.

When structuring larger commercial transactions or analyzing overall corporate tax strategy, corporate controllers often review broad fiscal obligations using the effective corporate tax rate calculator and assess funding structures with our after-tax cost of debt calculator.

Frequently asked questions