GST/Tax Calculator – Complete Guide & Free Online Tool
A GST/tax calculator adds tax to a price or extracts tax from a tax-inclusive price, showing the base amount, tax and total. Free online tool included.
Published 2026-09-13
What is GST/Tax Calculator?
A GST/tax calculator adds tax to a price or extracts tax from a tax-inclusive price, showing the base amount, tax and total.
Two modes
"Add tax" calculates base × (1 + rate/100). "Tax included" reverses this: base = total / (1 + rate/100), and tax = total − base.
Key Features
• Add or extract tax • Base • tax and total • Transparent calculation
Examples
• 18% tax on $1 • 000 adds $180 • total $1 • 180. • From $1 • 180 inclusive • base is $1 • 000 and tax $180.
Common Use Cases
• Invoicing • Pricing • Accounting
Tips & Best Practices
• Use tax included when the shelf price already includes tax.
Limitations
• Uses a single flat rate; some regions have tiered or multiple rates.
External Resources
Wikipedia: Goods and Services Tax