About This GST Calculator
This free online GST calculator lets you add GST to a base price or remove GST from an inclusive price in seconds. It automatically handles the CGST/SGST split for intrastate transactions and shows IGST for interstate transactions — the most common question people get wrong when billing.
What is GST?
Goods and Services Tax (GST) is India's unified indirect tax system, introduced on 1 July 2017. It replaced a fragmented system of central and state taxes including excise duty, VAT, service tax, and CST. GST operates on the principle of destination-based consumption tax — tax flows to the state where goods or services are consumed.
India follows a dual GST structure: the Central Government levies Central GST (CGST) and the respective state levies State GST (SGST) on intrastate transactions. For interstate supply of goods or services, Integrated GST (IGST) is levied by the Centre.
GST Slabs in India (FY 2025-26)
| GST Rate | Common Examples |
|---|---|
| 0% / Nil | Fresh vegetables, eggs, milk, bread, salt, rice (non-packaged) |
| 5% | Edible oils, sugar, tea, coffee, life-saving drugs, economy class air travel, packed food items |
| 12% | Processed and packaged foods, butter, cheese, mobile phones, business class air travel |
| 18% | Most services, electronics, computers, washing machines, soap, chemicals, construction services |
| 28% | Luxury cars, motorcycles above 350cc, aerated drinks, tobacco products, cement, paints |
How is GST Calculated? The Formula
Adding GST to a base price:
- GST Amount = Base Price × GST Rate ÷ 100
- Total (Inclusive) Price = Base Price + GST Amount
- Example: ₹10,000 base at 18% GST → GST = ₹1,800 → Total = ₹11,800
Removing GST from an inclusive price:
- Base Price = Inclusive Price × 100 ÷ (100 + GST Rate)
- GST Amount = Inclusive Price − Base Price
- Example: ₹11,800 inclusive at 18% GST → Base = 11,800 × 100 ÷ 118 = ₹10,000 → GST = ₹1,800
CGST + SGST vs IGST — Which Applies?
This is one of the most common compliance questions for GST-registered businesses:
- Intrastate supply (supplier and buyer in same state): CGST + SGST, each at half the applicable rate. At 18% total, CGST = 9% and SGST = 9%.
- Interstate supply (supplier and buyer in different states or Union Territories): IGST at the full applicable rate. At 18%, IGST = 18%.
- Import of goods/services: IGST applies as if it were an interstate supply.
The GST invoice must clearly state CGST/SGST or IGST as applicable. Using the wrong tax type can create ITC (Input Tax Credit) mismatches during reconciliation.
GST Registration — Who Must Register?
GST registration is mandatory if your annual aggregate turnover exceeds:
- ₹40 lakh for suppliers of goods (₹20 lakh for special category states)
- ₹20 lakh for service providers (₹10 lakh for special category states)
- Any turnover for e-commerce operators and sellers on e-commerce platforms
- Any turnover for inter-state suppliers, even if turnover is below threshold
Even if not mandatory, voluntary GST registration lets you claim Input Tax Credit and appear more credible to B2B buyers.
Input Tax Credit (ITC) — Reducing Your GST Outflow
Registered businesses can claim ITC — the GST paid on purchases can be offset against the GST payable on sales. This avoids the cascading effect of tax-on-tax. The net GST payable = Output GST (on sales) − Input GST (on purchases). Only GST paid on business-related purchases qualifies; GST on personal use is not available as ITC.