GST Calculator Guide: How to Calculate GST, Add It or Remove It, with Examples

Goods and Services Tax is charged on almost everything you buy or sell in India, and getting the arithmetic right matters for invoices, price lists and returns. The calculation itself is simple once you know which of two situations you are in: adding GST to a base price, or taking GST out of a price that already includes it.

The two formulas

• Add GST: GST amount = base price × rate ÷ 100. Final price = base price + GST amount.
• Remove GST: Base price = inclusive price × 100 ÷ (100 + rate). GST amount = inclusive price − base price.

The common error is subtracting the rate straight from the inclusive price. If a product costs ₹1,180 including 18% GST, the base is not ₹1,180 − 18% = ₹967.60. It is 1,180 × 100 ÷ 118 = ₹1,000, with ₹180 of GST. The GST calculator does both directions.

Worked examples

The rate slabs

After the GST rate rationalisation that took effect on 22 September 2025, most goods and services fall into two main rates, 5% and 18%, with a higher 40% rate for a short list of sin and luxury items. A 0% rate applies to exempt items, and a few goods such as gold and silver carry special lower rates. Rates are notified by the GST Council and the government, and individual items move between slabs, so always check the HSN or SAC code of your product on the official GST portal before you invoice.

CGST, SGST and IGST

The same total rate is split depending on where the buyer and seller are:

The total tax is the same either way. The split only decides which government receives it and what appears on the invoice.

Input tax credit: why businesses care

A registered business can subtract the GST it paid on purchases from the GST it collected on sales, and pay only the difference. If you collected ₹18,000 on sales in a month and paid ₹11,000 on inputs, you remit ₹7,000. Credit is available only if the supplier has filed their return and the purchase is for business use, so matching your purchase records with the portal each month is essential. Certain items, such as personal consumption and some motor vehicles and food expenses, are blocked.

What a correct invoice shows

• Supplier and buyer GSTIN (for registered buyers), invoice number and date.
• Description, HSN or SAC code, quantity and taxable value of each item.
• The rate and the amount of CGST, SGST or IGST separately.
• Place of supply and total invoice value.

If you want to check a GSTIN's format before you use it, the GST number validator verifies the structure, though it cannot confirm that the number is active. For late filing, the GST late fee calculator estimates the fee.

Do you need to register?

Registration is compulsory above an annual turnover threshold, which is higher for suppliers of goods than for services, and lower in special-category states. Some businesses must register regardless of turnover, such as those making inter-state supplies of goods in many cases and e-commerce sellers. Small businesses can opt for the composition scheme, paying a low flat percentage of turnover without claiming input credit. Thresholds and conditions change, so confirm them on the GST portal.

Pricing tips for small sellers

1. Decide whether your listed price is inclusive or exclusive and say so clearly.
2. For inclusive prices, work back to the base price as shown above, so your margin is not eaten by the tax.
3. Round at the invoice level, not for each line item, if your software allows it.
4. Keep invoices and returns for the period required by law.

This guide is general information, not tax advice. Consult a chartered accountant or GST practitioner for your situation.

Frequently asked questions

How do I calculate GST on a price?

Multiply the base price by the GST rate and divide by 100, then add it to the base price.

How do I remove GST from an inclusive price?

Multiply the inclusive price by 100 and divide by 100 plus the rate. For 18%, divide by 1.18.

What are the main GST rates now?

Most items are at 5% or 18%, with 40% on a short list of luxury and sin goods and 0% on exempt items. Check the notified rate for your HSN code.

What is the difference between CGST, SGST and IGST?

CGST and SGST are charged within a state and split the rate equally. IGST is charged on inter-state supply at the full rate.

What is input tax credit?

The GST paid on business purchases that you can subtract from the GST you collect on sales.

Is the GST amount a business cost?

For a registered business claiming credit, no. For consumers and unregistered buyers, it is part of the price.

Last reviewed 8 November 2026. Rates, limits and rules change, so confirm figures with the official source before you act.