How to Use a GST Calculator: Inclusive vs Exclusive

Every GST invoice comes down to one question: is the price you are quoting inclusive of GST or exclusive of it? Get this wrong and you either short-charge yourself or over-bill your customer. This guide explains both, with worked examples for every GST slab, and shows you how to get an error-free figure in seconds using our free GST calculator.

GST Exclusive: tax added on top

GST Exclusive means the quoted price does not include GST. You add the tax on top of the base price. This is the most common way B2B services are quoted in India.

Formula: GST Amount = (Base Price × GST%) / 100

Example (18% slab): You quote a client ₹10,000 exclusive of GST. GST = (10,000 × 18) / 100 = ₹1,800. The invoice total your customer pays is ₹11,800.

GST Inclusive: tax already baked in

GST Inclusive means the price the customer sees already contains the GST. This is typical for retail and B2C, where the shelf price is the final price. To find the tax, you "reverse-calculate" out of the total.

Formula: Base Price = Total × 100 / (100 + GST%), then GST Amount = Total − Base Price

Example (18% slab): A product retails at ₹11,800 inclusive of GST. Base = 11,800 × 100 / 118 = ₹10,000, so the GST portion is ₹1,800.

Worked examples across every GST slab

Using a base (exclusive) price of ₹1,000, here is what each of India's four main GST rates adds:

GST Slab	Base Price	GST Amount	Invoice Total
5%	₹1,000	₹50	₹1,050
12%	₹1,000	₹120	₹1,120
18%	₹1,000	₹180	₹1,180
28%	₹1,000	₹280	₹1,280

Splitting GST into CGST, SGST and IGST

The calculated GST amount is not always a single line on your invoice. How it splits depends on where your customer is:

• Intra-state sale (same state): the tax splits equally into CGST + SGST. An 18% total becomes 9% CGST + 9% SGST.
• Inter-state sale (different states): the full amount is charged as a single IGST line. 18% total = 18% IGST.

For the full breakdown, see our guide on CGST, SGST & IGST explained.

How to use the GST calculator

1. Open the free GST calculator.
2. Enter the amount and choose whether it is inclusive or exclusive of GST.
3. Pick the applicable slab (5%, 12%, 18% or 28%).
4. Read off the base price, GST amount, and total instantly.

From calculation to a compliant invoice

Knowing the numbers is only half the job — you still need them on a proper tax invoice with your GSTIN, HSN/SAC codes and the correct CGST/SGST/IGST split. Skip the spreadsheet and use our free GST invoice generator to create a GST-compliant invoice and download a professional PDF in minutes.