India GST Calculator — How to Calculate GST Online Free

India's Goods and Services Tax is one of the most ambitious indirect tax reforms ever implemented — a single unified tax that replaced over 17 different central and state levies overnight on 1 July 2017. For businesses, freelancers, and accountants working with Indian clients or suppliers, understanding how GST works is essential for correct invoicing, compliance, and cash flow planning. This guide explains the rate structure, the CGST/SGST/IGST split, registration requirements, and how to calculate GST at any slab rate.

What GST replaced — and why it matters

Before GST, India had a deeply fragmented indirect tax system. Businesses faced:

• Central taxes: Central Excise Duty, Service Tax, CVD (Countervailing Duty), SAD
• State taxes: VAT, Central Sales Tax (CST), Entry Tax, Octroi, Luxury Tax, Entertainment Tax, Purchase Tax

Each state had its own VAT rate schedules. A business selling goods across multiple states had to comply with 29 different VAT regimes. Cascading tax — paying tax on tax — inflated costs throughout the supply chain. GST eliminated all of this with a single registration, a common rate structure, and a seamless input tax credit mechanism that prevents tax cascading.

The transformation was not without challenges. The first two years saw significant teething problems with the GSTN (GST Network) portal, frequent rate revisions, and compliance difficulties for small businesses. But as of 2026, the system is substantially more stable and the input credit mechanism functions well for most registered businesses.

India's 5-slab GST rate structure

India uses five GST rate slabs. Understanding which slab applies to your goods or services is the first step in calculating the correct GST:

• 0% — No GST on essential goods: fresh fruits, vegetables, unbranded cereals, milk, eggs, unprocessed meat and fish, salt, bread (plain), educational services, and healthcare services. These are either exempt or zero-rated.
• 5% — Basic necessities that are processed or packaged: packaged food, edible oils, sugar, tea, coffee (except at restaurants), life-saving drugs, domestic LPG, economy class air travel, and railway transport.
• 12% — Mid-tier goods and services: processed and frozen food, smartphones, computers, business class air travel, non-AC hotel rooms (tariff below ₹7,500), and construction services for affordable housing.
• 18% — The standard rate applicable to most services: IT and software services, financial services, telecom, hair salons, AC restaurants, most manufactured goods, packaged goods, and mid-range electronics.
• 28% — Luxury and demerit goods: cars (plus GST Compensation Cess), SUVs, motorcycles above 350cc, tobacco and cigarettes, aerated drinks, large appliances, cement, and large-screen TVs. Many items at 28% carry an additional cess on top.

Use the India GST calculator to switch between slabs and calculate your exact GST instantly for any INR amount.

CGST, SGST, and IGST — the three-way split

GST revenue is shared between the Central Government and State Governments. How it splits depends on whether the transaction is intra-state or inter-state:

Intra-state supply (within the same state): GST is split equally into CGST (Central GST) and SGST (State GST). For an 18% GST transaction, the buyer pays 9% CGST + 9% SGST — two separate tax lines on the invoice, but same total for the buyer.

Inter-state supply (between different states) and imports: Only IGST (Integrated GST) applies at the full rate — 18% in the example above. The Central Government collects it and apportions the state's share to the destination state. This prevents the exporting state from benefiting at the expense of the importing state.

Worked examples at 18%:

• A Delhi consultancy invoices a Mumbai client for ₹1,00,000 (ex-GST): inter-state → IGST 18% = ₹18,000. Total = ₹1,18,000.
• A Bangalore freelancer invoices a Bangalore company for ₹50,000 (ex-GST): intra-state → CGST 9% (₹4,500) + SGST 9% (₹4,500) = GST ₹9,000. Total = ₹59,000.
• A manufacturer selling goods at ₹10,000 with 12% GST: GST = ₹1,200. Total = ₹11,200.

GST registration — who must register?

The mandatory registration threshold is ₹20 lakh annual aggregate turnover for most states. Two different thresholds apply in special cases:

• ₹10 lakh for special category states (Arunachal Pradesh, Assam, J&K, Manipur, Meghalaya, Mizoram, Nagaland, Sikkim, Tripura, Uttarakhand, and Himachal Pradesh)
• ₹40 lakh for businesses dealing exclusively in goods (not services) in most states — revised in 2019 to ease compliance for small goods traders

Some businesses must register regardless of turnover: inter-state suppliers, e-commerce operators (like those selling on Amazon or Flipkart), businesses under reverse charge, and input service distributors.

Registration is done online at gst.gov.in. You receive a 15-digit GSTIN within 7 working days. Once registered, you file:

• GSTR-1 (outward supplies) — monthly or quarterly
• GSTR-3B (summary return + tax payment) — monthly
• GSTR-9 (annual return) — once per year

How to add or remove GST from any amount

Adding GST to a net price:

• GST = Net × (rate ÷ 100). Total = Net × (1 + rate ÷ 100)
• At 18%: ₹25,000 net → GST = ₹4,500 → Total = ₹29,500
• At 28%: ₹2,00,000 net → GST = ₹56,000 → Total = ₹2,56,000

Removing GST from a gross (GST-inclusive) price:

• Net = Gross ÷ (1 + rate ÷ 100). GST = Gross − Net
• At 18%: ₹1,18,000 gross → Net = ₹1,18,000 ÷ 1.18 = ₹1,00,000. GST = ₹18,000.
• At 5%: ₹52,500 gross → Net = ₹52,500 ÷ 1.05 = ₹50,000. GST = ₹2,500.

For professional GST invoices — with GSTIN, CGST/SGST breakdowns, and PDF export — use the free invoice generator. Set the tax rate to match your GST slab and download a compliant invoice instantly.

Related tools

• India GST Calculator — Calculate GST at any slab rate (0%–28%) for any INR amount
• Global VAT Calculator — Calculate VAT and GST across multiple countries
• Free Invoice Generator — Create professional GST invoices and download as PDF