All Tools Compare Glossary Formulas Blog Contact
Be the first to rate
Back to Formulas
Tax Formula

GST Formula

Published on July 05, 2026 • Last updated July 05, 2026

Mathematical Equation

$$GST\ Amount = Original\ Cost \times \frac{GST\%}{100}$$ $$Total\ Price = Original\ Cost + GST\ Amount$$

Variable Definitions

Original Cost

Original Cost

Base pre-tax price of goods or services

GST%

GST%

Goods and Services Tax percentage rate

GST Amount

GST Amount

Tax amount charged on the transaction

Total Price

Total Price

Post-tax price paid by the customer

Detailed Explanation

Goods and Services Tax (GST) is a comprehensive indirect tax levied on the supply of goods and services. When computing transactions, you either add GST to find the final customer price, or subtract (remove) GST from the final retail price to find the pre-tax base cost.

How to Calculate: Step-by-Step

To Add GST: 1. Identify the base pre-tax cost. 2. Multiply the cost by the GST rate, then divide by 100 to get the GST amount. 3. Add the GST amount to the base cost. To Remove GST: 1. Identify the total price including GST. 2. Divide the total price by $(1 + \text{GST\%} / 100)$ to calculate the base cost. 3. Subtract the base cost from the total price to find the GST amount.

Worked Calculation Example

Adding 18% GST to a base service worth $1,000: - Base Cost = $1,000 - GST Rate = 18% - GST Amount = $1,000 × (18 / 100) = $180 - Total Price = $1,000 + $180 = $1,180 Removing 18% GST from a retail item priced at $1,180: - Total Price = $1,180 - Base Cost = $1,180 / (1 + 18/100) = $1,180 / 1.18 = $1,000 - GST Amount = $1,180 - $1,000 = $180

Common Use Cases

  • Calculating product retail prices including VAT/GST
  • Filing business sales tax returns and invoicing customers
  • Removing tax from items to understand the actual manufacturing base price

Frequently Asked Questions

CGST (Central GST) and SGST (State GST) are levied on intra-state transactions (within the same state) and split equally. IGST (Integrated GST) is levied on inter-state transactions and collected by the central government.

Input Tax Credit allows a business to reduce the GST paid on purchases from the GST liability it collects on sales, effectively taxing only the value added at that stage.

Free Forever • No Limits

Your everyday toolkit,
always within reach

Bookmark EasyToolio and access 125 tools whenever you need them. Calculate, decide, generate — all for free.

Try Decision Wheel