Whether you’re a business owner setting prices, a freelancer invoicing clients, or a consumer checking a receipt, understanding how GST and VAT work is essential. This guide explains the difference between tax-inclusive and tax-exclusive prices and shows you the exact formulas to add or remove tax correctly.

What Are GST and VAT?

GST (Goods and Services Tax) and VAT (Value Added Tax) are consumption taxes applied to goods and services. They work the same way mathematically — the difference is mainly in name and regional usage:

VAT is used in the European Union, UK, Australia (historically), and many other countries
GST is used in India, Canada, Australia, Singapore, and New Zealand
Sales Tax (US) is similar but applied only at the final point of sale

Common Tax Rates Worldwide

Country/Region	Tax Name	Standard Rate
European Union	VAT	17-27%
United Kingdom	VAT	20%
India	GST	5-28% (18% standard)
Australia	GST	10%
Canada	GST/HST	5-15%
Singapore	GST	9%
New Zealand	GST	15%
Japan	Consumption Tax	10%
United States	Sales Tax	0-10.25% (varies by state)

Adding Tax to a Price (Tax-Exclusive)

When a price does not include tax, you add tax to get the total:

Total Price = Net Price × (1 + Tax Rate / 100)

Tax Amount = Net Price × Tax Rate / 100

Example

A product costs $100 (before tax) with 18% GST:

Tax Amount = $100 × 0.18 = $18
Total Price = $100 × 1.18 = $118

Removing Tax from a Price (Tax-Inclusive)

When a price already includes tax and you need to find the pre-tax amount:

Net Price = Total Price ÷ (1 + Tax Rate / 100)

Tax Amount = Total Price - Net Price

Example

A product costs $118 (tax-inclusive) with 18% GST:

Net Price = $118 ÷ 1.18 = $100
Tax Amount = $118 - $100 = $18

Common Mistake

Many people incorrectly calculate the tax amount by multiplying the total by the tax rate:

❌ Wrong: Tax = $118 × 18% = $21.24 (too much!) ✅ Correct: Tax = $118 - ($118 ÷ 1.18) = $18

The wrong method overstates the tax by $3.24. On a $10,000 invoice, this error would cost you $270.

Quick Reference Formulas

What You Need	Formula
Add tax	Net × (1 + Rate/100)
Remove tax	Total ÷ (1 + Rate/100)
Tax amount (from net)	Net × Rate/100
Tax amount (from total)	Total - Total ÷ (1 + Rate/100)
Net from tax amount	Tax ÷ (Rate/100)

Business Scenarios

Setting Retail Prices

If you want customers to pay $99 (tax-inclusive) and GST is 10%:

Net Price = $99 ÷ 1.10 = $90
Your revenue (before remitting tax) = $90
You collect $9 in GST to remit to the government

Invoice Calculation

For a $5,000 service with 20% VAT:

Subtotal: $5,000
VAT (20%): $1,000
Total: $6,000

Reverse Calculation for Receipts

Your restaurant bill is $85 including 10% GST:

Net amount: $85 ÷ 1.10 = $77.27
GST: $85 - $77.27 = $7.73

Compound Tax Situations

Some regions apply multiple taxes. For example, in Canada, you may pay both GST (5%) and PST (7%):

Total = Net × (1 + GST/100) × (1 + PST/100)

Or if they’re combined as HST: Total = Net × (1 + HST/100)

For a $100 item with 5% GST + 7% PST:

After GST: $100 × 1.05 = $105
After PST: $105 × 1.07 = $112.35

Note: PST is sometimes calculated on the GST-inclusive amount, not the net amount. Check your local regulations.

Tax Exemptions and Reduced Rates

Most GST/VAT systems have reduced rates or exemptions for essentials:

Zero-rated (0%): Basic groceries, prescription medicines, exports
Reduced rate: Books, children’s clothing, domestic energy
Exempt: Financial services, healthcare, education

Always check which rate applies to your specific goods or services before calculating.

Calculate GST/VAT Instantly

Don’t risk calculation errors on your invoices. Use our free GST Calculator to add or remove GST/VAT from any amount instantly. Enter the amount and tax rate, choose whether to add or remove tax, and get accurate results every time.

Perfect for invoicing, receipt checking, and price setting.