GST Calculator

The GST calculator is one of the most commonly used finance tools in India because GST shows up on almost every invoice, restaurant bill, e-commerce order, utility bill and service quote. Knowing how to calculate GST correctly — both adding it to a base price and extracting it from an inclusive amount — is essential for individuals checking their bills, freelancers issuing invoices, small business owners pricing products, and anyone evaluating a quote.

Goods and Services Tax replaced a tangle of central excise, state VAT, service tax, octroi and entry taxes in July 2017. It is a single, unified, destination-based tax on the supply of goods and services across India. Every registered business with annual turnover above ₹40 lakh (₹20 lakh for service providers in most states) must register for GST and charge the applicable rate on every transaction.

GST has four standard rate slabs in India: 5%, 12%, 18% and 28%. The 5% slab covers essentials and mass-market services such as packaged food items, footwear under ₹1,000, economy class air tickets, restaurant takeaway and small hotel rooms (under ₹7,500/night). The 12% slab covers processed food, business class air tickets and a number of intermediate categories. The 18% slab is the default for most goods and services including soaps, computers, telecom services, banking and insurance services, restaurants in larger hotels, and most professional services. The 28% slab is reserved for luxury and sin goods including cars, air conditioners, refrigerators, premium hotels, betting and tobacco — many of which also attract an additional cess on top.

A small set of items is GST-exempt: fresh fruits and vegetables, milk, education services, healthcare services, books and newspapers. Petrol, diesel, crude oil, natural gas and aviation turbine fuel are still outside GST and continue to be taxed under the older state VAT and central excise regime — which is why fuel prices vary widely between states.

Use this calculator in two modes. The 'add GST' mode is for businesses pricing a product or service: enter the base price and the applicable rate, and the calculator returns the GST amount and the final tax-inclusive price. The 'remove GST' mode is for consumers checking an inclusive bill: enter the total amount and the rate, and the calculator extracts the base price and the embedded GST amount. The mathematical formulas are different in each direction — a common mistake is to apply the rate as a discount rather than dividing by (100 + rate), which gives a wrong answer.

Intra-state versus inter-state matters for understanding your invoice but not for the total amount. When the seller and the buyer are in the same state, the GST is split equally into Central GST (CGST) and State GST (SGST) — so 18% GST shows up as 9% CGST plus 9% SGST. When the seller and the buyer are in different states, the entire GST is charged as Integrated GST (IGST). The total rate and the total amount are the same; only the accounting head differs.

A valid B2B GST invoice must show: seller's name and GSTIN, buyer's name and GSTIN, place of supply, HSN code (for goods) or SAC code (for services), taxable value, GST rate, GST amount split into CGST/SGST or IGST, and the total. For B2C invoices above ₹50,000, the buyer's name and address are required. The GSTIN itself is a 15-character code: 2 digits for state, 10 for the company's PAN, 1 entity code, 1 default digit and 1 check digit.

For freelancers and small service providers, the composition scheme is worth knowing. Businesses with turnover under ₹1.5 crore (₹50 lakh for services) can opt for a flat 1-6% GST without input tax credit. Composition dealers cannot show GST on their invoice and cannot collect it from the customer — the tax is paid out of their own margins. For most B2C service providers this can be simpler and cheaper than regular GST.

Finally, GST input tax credit is the magic that prevents the tax from cascading. A business pays GST on its inputs (raw materials, services, equipment) and collects GST on its outputs (sales). It only pays the difference to the government. This is why aggregating goods through GSTN-linked suppliers genuinely reduces the wholesale price across the supply chain compared to the pre-GST regime.