Real GSTCalculator
Formulas & Worked Examples

GST Calculator Formula & Calculations

Everything you need to know about the GST calculator formula and its math in India. Learn how to add or remove tax easily using our step-by-step guide and interactive playground.

1. GST Calculator Formula for Exclusive Tax (Adding GST)

Used when you know the base taxable cost of goods or services and want to add tax on top.

GST Amount = Taxable Value × (GST Rate ÷ 100)
Total Amount (Gross) = Taxable Value + GST Amount

Worked Example:

Scenario: Taxable value = ₹10,000, GST rate = 18%

  • GST Amount = ₹10,000 × (18 ÷ 100) = ₹1,800
  • Total Amount = ₹10,000 + ₹1,800 = ₹11,800

2. GST Calculator Formula for Inclusive Tax (Extracting GST / Reverse GST)

Used when a price already contains the tax component and you want to extract the underlying taxable amount and the GST value.

Taxable Value = Total Amount × 100 ÷ (100 + GST Rate)
GST Amount = Total Amount − Taxable Value

Worked Example:

Scenario: Total amount = ₹11,800 (inclusive of 18% GST)

  • Taxable Value = ₹11,800 × 100 ÷ (100 + 18) = ₹10,000
  • GST Amount = ₹11,800 − ₹10,000 = ₹1,800

3. Tax Splits: Intra-State vs. Inter-State

Once you calculate the GST Amount, it is split depending on where the transaction occurs:

Intra-State (Within same state): CGST = SGST = GST Amount ÷ 2
Inter-State (To another state): IGST = GST Amount

Worked Example:

Scenario: GST Amount = ₹1,800

  • Local Sale: CGST = ₹900, SGST = ₹900
  • Inter-state Sale: IGST = ₹1,800

Interactive Formula Playground

Type in an amount and change the rate to see the formulas calculate in real-time, step-by-step.

Exclusive GST Step-by-Step

Inclusive GST Step-by-Step

Frequently Asked Questions

What is the formula to calculate GST?

For adding GST (exclusive): GST Amount = Taxable Value × GST Rate ÷ 100. For extracting GST (inclusive): GST Amount = Total Amount − [Total Amount × 100 ÷ (100 + GST Rate)].

How is CGST and SGST calculated?

For local or intra-state sales, the GST rate is divided equally. CGST = SGST = GST Amount ÷ 2. For example, an 18% GST rate splits into 9% CGST and 9% SGST.

What is reverse GST calculation?

Reverse GST calculation is the process of finding the original taxable amount before tax was added. The formula is: Taxable Amount = Inclusive Amount × 100 ÷ (100 + GST Rate).