GST (Goods and Services Tax) was introduced in India on 1 July 2017, replacing a complex system of multiple indirect taxes. Since then, every business owner, freelancer, trader, and accountant in India needs to understand how to calculate GST on their transactions. This guide explains the GST formula, all tax slabs, how to compute CGST/SGST/IGST, and walks through real-world examples you can follow immediately.
Free GST Calculator — CGST, SGST & IGST Breakdown
Calculate GST on any amount instantly. Shows CGST, SGST, IGST split. GST inclusive and exclusive modes. Free, no signup.
What Is GST and Why Does It Matter?
GST is a comprehensive, multi-stage, destination-based tax levied on every value addition in the supply chain. In simple terms, it replaces excise duty, VAT, service tax, and 17 other taxes with a single unified tax.
Three types of GST in India
| Type | Full Form | When Applied | Who Collects |
|---|---|---|---|
| CGST | Central GST | Intra-state supply | Central Government |
| SGST | State GST | Intra-state supply | State Government |
| IGST | Integrated GST | Inter-state supply / Imports | Central Government |
Key rule: For intra-state transactions (buyer and seller in same state), CGST + SGST applies. Each is half the total GST rate. For inter-state transactions (different states), IGST applies at the full rate.
GST rate slabs in India (2025-26)
| GST Rate | Examples of Goods/Services |
|---|---|
| 0% (Exempt) | Fresh fruits, vegetables, milk, eggs, unbranded cereals, healthcare services, educational services |
| 5% | Household essentials — sugar, edible oil, tea, coffee, coal, medicines, economy class air tickets |
| 12% | Processed food, butter, cheese, mobile phones, business class air tickets, non-AC restaurants |
| 18% | Most services — IT services, restaurants, financial services, most manufactured goods, telecom |
| 28% | Luxury goods — cars, motorcycles >350cc, tobacco, aerated drinks, casinos, 5-star hotels |
GST Calculation Formula — Step by Step
There are two scenarios for GST calculation depending on whether the price given is exclusive (before GST) or inclusive (after GST already added).
Case 1: GST Exclusive — Adding GST to the Base Price
Use this when you know the price before GST and need to find the final price and tax amount.
GST Amount = (Base Price × GST Rate) ÷ 100
Final Price = Base Price + GST AmountYou are a software company billing a client ₹50,000 for development services (GST rate: 18%).
- GST Amount = (50,000 × 18) ÷ 100 = ₹9,000
- Final Invoice Amount = 50,000 + 9,000 = ₹59,000
- Since this is an intra-state transaction: CGST = ₹4,500, SGST = ₹4,500
Case 2: GST Inclusive — Extracting GST from a Total Price
Use this when the price you paid already includes GST and you need to find the original base price and tax amount separately.
Base Price = (Inclusive Price × 100) ÷ (100 + GST Rate)
GST Amount = Inclusive Price - Base PriceYou bought a restaurant meal for ₹1,180 (GST inclusive at 18%).
- Base Price = (1,180 × 100) ÷ (100 + 18) = 1,18,000 ÷ 118 = ₹1,000
- GST Amount = 1,180 − 1,000 = ₹180
- CGST = ₹90, SGST = ₹90
IGST vs CGST + SGST — Calculation Examples
Understanding when to apply IGST vs CGST+SGST is essential for invoicing and tax filing.
Intra-state transaction (same state) — CGST + SGST
A Mumbai-based supplier sells goods worth ₹1,00,000 to a Mumbai buyer at 18% GST:
- CGST (9%) = ₹9,000 → goes to Central Government
- SGST (9%) = ₹9,000 → goes to Maharashtra Government
- Total GST = ₹18,000 | Invoice Amount = ₹1,18,000
Inter-state transaction (different states) — IGST
A Delhi supplier sells goods worth ₹1,00,000 to a Bengaluru buyer at 18% GST:
- IGST (18%) = ₹18,000 → goes to Central Government, later shared with Karnataka
- Invoice Amount = ₹1,18,000
- No separate CGST or SGST on this invoice
| Scenario | Tax Applied | Split |
|---|---|---|
| Supplier and buyer in same state | CGST + SGST | Each = half the GST rate |
| Supplier and buyer in different states | IGST | Full GST rate as one tax |
| Import (from outside India) | IGST + Customs Duty | IGST = full rate on CIF value |
| Export (to outside India) | 0% GST (zero-rated) | Refund of input tax credit |
GST Registration: Who Must Register?
Not every business needs to register for GST. Here are the current thresholds as of FY 2025-26:
| Business Type | Annual Turnover Threshold |
|---|---|
| Regular businesses (goods supply) | Above ₹40 lakh |
| Regular businesses (services / goods in special category states) | Above ₹20 lakh |
| North-East states + special category states (all) | Above ₹10 lakh |
| E-commerce operators / sellers on Amazon, Flipkart, Meesho | Mandatory regardless of turnover |
| Inter-state suppliers | Mandatory regardless of turnover |
| Casual taxable persons | Mandatory regardless of turnover |
If you sell on any e-commerce marketplace (Amazon, Flipkart, Meesho, Myntra), GST registration is mandatory from the first rupee of sales — regardless of your annual turnover. Not registering can result in penalties and account suspension.
GST Quick Reference Calculations
Common GST calculations for reference:
| Base Amount | GST Rate | GST Amount | Total Invoice |
|---|---|---|---|
| ₹1,000 | 5% | ₹50 | ₹1,050 |
| ₹1,000 | 12% | ₹120 | ₹1,120 |
| ₹1,000 | 18% | ₹180 | ₹1,180 |
| ₹1,000 | 28% | ₹280 | ₹1,280 |
| ₹10,000 | 18% | ₹1,800 | ₹11,800 |
| ₹50,000 | 18% | ₹9,000 | ₹59,000 |
| ₹1,00,000 | 18% | ₹18,000 | ₹1,18,000 |
ToolsArena's free GST Calculator handles all these calculations instantly — just enter the base amount and select the GST rate. It shows CGST, SGST, and IGST breakdowns automatically.
How to Use the Tool (Step by Step)
- 1
Open the GST Calculator
Go to ToolsArena's GST Calculator. No login or account needed.
- 2
Enter the base amount
Type the price before GST (exclusive) or the total price including GST (inclusive) — select the mode accordingly.
- 3
Select the GST rate
Choose 5%, 12%, 18%, or 28% from the dropdown based on the goods or service category.
- 4
Choose GST type
Select "GST Exclusive" if your price does not include GST, or "GST Inclusive" if your price already includes GST.
- 5
Read the breakdown
The calculator shows GST amount, CGST, SGST (for intra-state), and IGST (for inter-state), plus the final total amount.
Frequently Asked Questions
How do I calculate 18% GST on ₹1,000?+−
GST Amount = (1,000 × 18) ÷ 100 = ₹180. Final price = 1,000 + 180 = ₹1,180. For intra-state: CGST = ₹90, SGST = ₹90. For inter-state: IGST = ₹180.
How do I calculate GST when the price is inclusive?+−
Use the reverse formula: Base Price = (Inclusive Price × 100) ÷ (100 + GST Rate). Example: Item costs ₹1,180 with 18% GST inclusive. Base Price = (1,180 × 100) ÷ 118 = ₹1,000. GST = ₹180.
What is the GST rate on software services / IT services?+−
IT and software services are taxed at 18% GST (SAC code 998314–998319 for software development, IT consulting, and related services). This applies to freelancers, agencies, and software companies. If you export services to foreign clients, it qualifies as "export of services" and is zero-rated (0% GST).
Is GST applicable on freelance income in India?+−
Yes, if your annual turnover from freelance services exceeds ₹20 lakh (₹10 lakh in special category states), you must register for GST. Below this threshold, GST is optional. Once registered, you charge 18% GST on your invoices and file quarterly/monthly GST returns.
What is the difference between GST and TDS?+−
GST is an indirect tax on goods and services — it is added to the invoice and collected from the buyer. TDS (Tax Deducted at Source) is a direct tax deducted by the buyer from the payment amount before paying the seller. Both can apply to the same transaction. Example: A company paying ₹1,18,000 to a service provider (₹1,00,000 + ₹18,000 GST) may deduct TDS of 10% on ₹1,00,000 = ₹10,000, paying only ₹1,08,000 and depositing ₹10,000 TDS with the government.
Free GST Calculator — CGST, SGST & IGST Breakdown
Calculate GST on any amount instantly. Shows CGST, SGST, IGST split. GST inclusive and exclusive modes. Free, no signup.
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