Comprehensive GST & Sales Tax Calculator

Whether you are a small business owner issuing invoices, an accountant balancing the books, or a consumer trying to figure out the true cost of an item, our GST (Goods and Services Tax) calculator is the ultimate tool. It allows you to seamlessly add tax to a base amount or extract the hidden tax from a final inclusive price.

How Sales Tax & GST is Calculated (The Formulas)

Many people make the mathematical error of simply subtracting the tax percentage from the final price to find the base price. This is mathematically incorrect. Here are the proper formulas used by accountants:

To Add Tax (Exclusive to Inclusive):

When you have a base price and need to add the tax on top of it:

• Tax Amount = Base Price × (Tax Percentage / 100)
• Final Price = Base Price + Tax Amount
• Example: A $200 item with 10% GST. 200 × 0.10 = $20. The Final Price is $220.

To Remove Tax (Inclusive to Exclusive):

When you have the final receipt price and need to find out what the item cost before tax (reverse calculating):

• Base Price = Final Price / (1 + (Tax Percentage / 100))
• Tax Amount = Final Price - Base Price
• Example: You paid $220 total, which includes 10% GST. 220 / 1.10 = $200. The Base Price is $200, and the tax was $20.

Global Tax Systems Reference

• Australia/New Zealand: 10% to 15% standard GST applied to most goods and services.
• Canada: Uses a mix of federal GST (5%) and provincial PST, sometimes combined into an HST (Harmonized Sales Tax) up to 15%.
• Europe (VAT): Value Added Tax varies wildly by country, often ranging from 17% to 25%.
• United States: Uses state and local Sales Tax (not a federal VAT/GST), ranging from 0% (e.g., Oregon) up to nearly 10% in some municipalities.

Frequently Asked Questions

Why can't I just subtract 10% from the total to find the base price?
Because the 10% tax was calculated based on the smaller base number, not the larger final number! 10% of 220 is 22, meaning 220 - 22 = 198 (which is incorrect, the base was 200).