How to Calculate GST: Formula, Examples & GST Rates in India

What is GST?

GST stands for Goods and Services Tax. It is an indirect tax charged on the supply of goods and services in India.

For example, suppose you sell a product for ₹1,000 and GST is 18%. The GST amount would be ₹1,000 × 18% = ₹180, so the customer pays ₹1,000 + ₹180 = ₹1,180. That is the basic idea behind GST calculation.

GST Calculation Formula

When the price is before GST, you can use this simple formula:

GST Amount = Original Price × GST Rate ÷ 100

And: Final Price = Original Price + GST Amount

Example: 18% GST

Suppose a product costs ₹2,500 before GST and the GST rate is 18%.

GST amount: ₹2,500 × 18 ÷ 100 = ₹450.

Final price: ₹2,500 + ₹450 = ₹2,950.

So the customer pays ₹2,950, including ₹450 GST.

How to Calculate GST Quickly

Imagine you are selling a service for ₹5,000 and GST is 18%. You do not need a complicated calculation.

₹5,000 × 18% = ₹900 GST. Then add the GST to the original amount: ₹5,000 + ₹900 = ₹5,900.

So the original price is ₹5,000, the GST is ₹900, and the final price is ₹5,900. For repeated calculations, our GST Calculator can do this automatically.

How to Calculate GST Inclusive Price

This is where things can get a little confusing. Sometimes the price you see already includes GST. For example, you have a bill of ₹1,180 including 18% GST.

You cannot simply calculate 18% of ₹1,180 and call that the GST amount. That would give the wrong result.

When GST is already included in the price, use this formula: Original Price = Inclusive Price × 100 ÷ (100 + GST Rate).

For 18% GST: Original Price = ₹1,180 × 100 ÷ 118 = ₹1,000. Now GST = ₹1,180 − ₹1,000 = ₹180. So the original price was ₹1,000 and the GST included in ₹1,180 was ₹180. This is commonly called reverse GST calculation.

If you regularly need to remove GST from an inclusive amount, you can use the GST Calculator instead of doing the calculation manually.

GST Exclusive vs GST Inclusive

The easiest way to understand the difference is with an example. Suppose the product price is ₹1,000 and GST is 18%.

GST Exclusive means ₹1,000 is the price before GST. GST = ₹180 and the final price = ₹1,180.

GST Inclusive means ₹1,180 is the price already including GST. The actual product price = ₹1,000 and the GST included = ₹180.

So the same ₹1,180 can represent either a final price including GST, or a price that still needs GST added, depending on how the price was given to you. That is why it is important to know whether a quoted price is inclusive or exclusive of GST.

How to Calculate CGST and SGST

For an intra-state supply, GST may be divided into CGST and SGST. For example, suppose the total GST rate is 18%. It can be divided as CGST = 9% and SGST = 9%.

Suppose the taxable value is ₹10,000. CGST: ₹10,000 × 9% = ₹900. SGST: ₹10,000 × 9% = ₹900. Total GST: ₹900 + ₹900 = ₹1,800. Final amount: ₹10,000 + ₹1,800 = ₹11,800.

So for an 18% GST rate in this example, the tax is split equally between CGST and SGST.

What is IGST?

IGST stands for Integrated Goods and Services Tax. For an applicable inter-state supply, GST is generally charged as IGST rather than being split into CGST and SGST on the invoice.

For example, if the taxable value is ₹10,000 and the applicable GST rate is 18%: IGST = ₹10,000 × 18% = ₹1,800. Total invoice amount: ₹10,000 + ₹1,800 = ₹11,800.

So CGST + SGST commonly applies to intra-state supplies, and IGST commonly applies to inter-state supplies. The actual tax treatment depends on the nature and place of supply, so businesses should follow the applicable GST rules for their transaction.

How to Calculate 18% GST

18% is one of the GST rates you will commonly come across. The calculation is straightforward. Suppose the taxable amount is ₹3,000.

₹3,000 × 18 ÷ 100 = ₹540 GST. Final price: ₹3,000 + ₹540 = ₹3,540.

Quick examples: a ₹500 supply at 18% gives ₹90 GST and a ₹590 final price; ₹1,000 gives ₹180 GST and ₹1,180 final; ₹2,000 gives ₹360 GST and ₹2,360 final; ₹5,000 gives ₹900 GST and ₹5,900 final; and ₹10,000 gives ₹1,800 GST and ₹11,800 final. The same basic formula can be used for other applicable GST rates as well.

How to Calculate GST at 5%, 12%, 18% and 28%

Once you know the formula, changing the GST rate is easy. Suppose the taxable value is ₹1,000.

At 5%: GST = ₹50 and final price = ₹1,050. At 12%: GST = ₹120 and final price = ₹1,120. At 18%: GST = ₹180 and final price = ₹1,180. At 28%: GST = ₹280 and final price = ₹1,280.

Keep in mind that the applicable GST rate depends on the goods or services involved. Do not choose a rate simply because it is commonly used.

How to Remove GST From a Price

Let us say you have a final price of ₹5,900, including 18% GST, and you want to find the original price before GST.

Use: Original Price = Inclusive Price × 100 ÷ (100 + GST Rate). So ₹5,900 × 100 ÷ 118 = ₹5,000. GST = ₹5,900 − ₹5,000 = ₹900.

Therefore the price before GST is ₹5,000, the GST is ₹900, and the price including GST is ₹5,900. This is why reverse GST calculation is different from simply subtracting 18% from the final price.

Why Use a GST Calculator?

Manual GST calculations are easy when you are checking one or two amounts. But if you are working with multiple products, invoices, quotations, or selling prices, doing every calculation manually can become tedious.

A GST calculator can help you quickly find GST added to a price, GST included in a price, the final price after GST, the CGST and SGST split, the IGST amount, and different GST rates.

GST Calculation: A Simple Example

Suppose you are selling a product for ₹7,500 before GST, and the applicable GST rate is 18%.

Step 1: Calculate GST. ₹7,500 × 18 ÷ 100 = ₹1,350. Step 2: Add GST. ₹7,500 + ₹1,350 = ₹8,850. So the final price is ₹8,850.

If the transaction is one where the GST is split equally into CGST and SGST: CGST at 9% = ₹675 and SGST at 9% = ₹675, for a total GST of ₹1,350. Again, the actual treatment depends on the transaction and applicable GST rules.

Frequently Asked Questions

How do I calculate GST on a price? If the price is before GST, use GST = Price × GST Rate ÷ 100, then add the GST amount to the original price to get the final amount.

How do I calculate GST from an inclusive price? Use Original Price = Inclusive Price × 100 ÷ (100 + GST Rate), then subtract the original price from the inclusive price to find the GST amount.

How do I calculate 18% GST? Multiply the taxable amount by 18 and divide by 100. For ₹1,000: ₹1,000 × 18 ÷ 100 = ₹180.

Is CGST always half of GST? For an applicable intra-state supply where the GST rate is split equally, an 18% GST rate can be divided into 9% CGST and 9% SGST. The exact treatment depends on the applicable tax rules.

What is the difference between CGST, SGST and IGST? CGST and SGST can apply together to an applicable intra-state supply, while IGST generally applies to an applicable inter-state supply.

Calculate GST Online

If you already know the amount and GST rate, there is no need to work through the formulas every time. Use our GST Calculator to calculate GST, work backwards from an inclusive price, and see the applicable tax split where supported.

You can also compare the result with your own calculation to make sure you have entered the correct amount and GST rate.