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What Is GST and How Does It Work? A Complete Guide

GST (Goods and Services Tax) is a broad-based consumption tax applied to most goods and services at each stage of the supply chain. Unlike older sales tax systems that taxed at multiple levels (causing tax-on-tax), GST uses an input tax credit mechanism that allows businesses to claim credits for GST already paid on inputs, so the tax is ultimately borne only by the end consumer.

Over 160 countries have adopted some form of GST or VAT (Value Added Tax). This guide covers the GST systems in India, Canada, Australia, and New Zealand — the four countries supported by our free GST calculator.

How to Calculate GST: The Two Formulas

There are two common GST calculations:

1. Add GST (Exclusive to Inclusive)

When you have a base price before tax and need to find the GST-inclusive total:

Example: A product costs ₹10,000 before 18% GST.
GST = ₹10,000 × 0.18 = ₹1,800
Final Price = ₹10,000 + ₹1,800 = ₹11,800

2. Remove GST (Inclusive to Exclusive)

When you have a GST-inclusive total and need to find the original base price:

Example: A receipt shows $115 including 15% NZ GST.
Base Price = $115 / 1.15 = $100
GST = $115 − $100 = $15

India GST: Slabs, Structure & GST 2.0 Reform

India introduced GST on July 1, 2017, replacing 17 central and state taxes. Following the GST 2.0 reform in September 2025, the slab structure was simplified from 5 slabs to 4:

India's GST is further split into CGST (Central GST) and SGST (State GST) for intra-state transactions, or IGST (Integrated GST) for inter-state transactions. The total rate remains the same — for example, 18% GST = 9% CGST + 9% SGST.

Source: CBIC GST Portal

Canada GST/HST/PST: A Provincial Breakdown

Canada's sales tax system is uniquely complex because it combines a federal GST (5%) with varying provincial taxes:

In HST provinces (Ontario, Nova Scotia, New Brunswick, Newfoundland, PEI), the federal and provincial taxes are combined into a single Harmonized Sales Tax collected by the CRA. In other provinces, the PST/RST/QST is collected separately by the provincial government.

Source: Canada Revenue Agency (CRA)

Australia GST: How the 10% Rate Works

Australia has had a flat 10% GST since July 2000. It applies to most goods, services, and imports. Key exemptions include:

• GST-free: Basic food, most health and medical services, education, childcare, exports
• Input-taxed: Financial services, residential rent — no GST charged but no input credits available

Businesses with annual turnover of $75,000 or more ($150,000 for non-profits) must register for GST. Registered businesses charge 10% GST on taxable supplies and can claim input tax credits for GST paid on business purchases.

Source: Australian Taxation Office (ATO)

New Zealand GST: The Broadest in the World

New Zealand's 15% GST is notable for having very few exemptions — making it one of the cleanest and broadest consumption taxes globally. Key features:

• Exempt: Financial services, residential rent, donations
• Zero-rated (0%): Exports, international transport, supply of a going concern
• Everything else: 15% — including most food, clothing, electronics, and professional services

Businesses with annual taxable supplies over NZ$60,000 must register for GST. Returns are filed two-monthly, six-monthly, or monthly depending on turnover.

Source: Inland Revenue Department (IRD)

GST vs VAT vs Sales Tax: What's the Difference?

These terms are often used interchangeably, but there are structural differences:

• GST (India, Canada, Australia, NZ, Singapore, Malaysia): A multi-stage consumption tax with input credit mechanism. Tax is collected at each supply chain stage but only the value added is effectively taxed.
• VAT (EU, UK, China, South Africa): Functionally identical to GST. The name "Value Added Tax" is more common in Europe. The UK's standard VAT is 20%, the EU averages 20-27%.
• Sales Tax (US states): Charged only at the final point of sale to the end consumer. No input credit mechanism. US states range from 0% to 10.25% combined rates.

The key advantage of GST/VAT over sales tax is self-policing — each business in the chain has an incentive to ensure the previous business charged and remitted the correct tax, because their own input credits depend on it.

How to Calculate GST for Business Invoices

If you're a business issuing invoices, here's how GST typically works:

1. Determine taxability: Is the good/service taxable, exempt, or zero-rated in your jurisdiction?
2. Apply the correct rate: In India, identify the HSN/SAC code to find the applicable slab. In Canada, determine whether HST or GST+PST applies based on the customer's province.
3. Show GST separately: Tax invoices must show the GST amount as a separate line item. In India, CGST and SGST (or IGST) must be shown individually.
4. Claim input credits: GST paid on business inputs can be claimed as Input Tax Credit (ITC), reducing your net GST liability.

Our GST calculator handles the math for step 2 — but always verify the applicable rate for your specific product or service category.

Common GST Exemptions by Country

Who Should Use a GST Calculator?

• Small business owners creating invoices and quotes with correct tax amounts
• Freelancers and contractors determining how much GST to add to their service fees
• Accountants and bookkeepers verifying GST calculations on client invoices
• Consumers checking if they're being charged the correct GST rate
• E-commerce sellers calculating final prices for different countries/provinces
• Importers/exporters determining GST on cross-border transactions
• Students learning how consumption taxes work across different countries