GST Calculation Guide: IGST vs. CGST vs. SGST Explained
Learn how GST works, understand IGST, CGST, and SGST differences, and use our calculator to compute taxes on your transactions.
If you're doing business in India, GST (Goods and Services Tax) affects every transaction. But the three types of GST — IGST, CGST, and SGST — confuse most people.
The difference matters. Apply the wrong GST type, and you could face penalties. Get it right, and you optimize your compliance and costs.
In this guide, we'll explain how GST works, clarify the three types, show you how to calculate each, and help you determine which applies to your transaction.
Why GST Matters
GST is India's most important indirect tax. Understanding it helps you:
- Calculate correct prices — know what to charge customers
- File returns accurately — avoid penalties and rejections
- Claim input credits — reduce your tax liability
- Plan business structure — decide if GST registration is beneficial
- Avoid penalties — comply with tax requirements
- Understand your costs — factor taxes into profitability
- Make pricing decisions — know the tax impact on margins
Most small businesses get GST wrong, costing them money or creating compliance issues. Those who understand it optimize both compliance and profitability.
What Is GST?
GST (Goods and Services Tax) is India's unified indirect tax on goods and services, effective since July 1, 2017.
Key Features:
- Single national tax (replaced 13+ state/central taxes)
- Destination-based consumption tax
- Tax collected at each step of supply
- Input credits allow cancellation of cascading taxes
- Applicability: Goods, services, and imports
Tax Structure:
- Central: CGST (Central GST)
- State: SGST (State GST)
- Interstate: IGST (Integrated GST)
Total tax rate: 5%, 12%, 18%, or 28% (depending on product/service)
CGST, SGST, and IGST: The Differences
CGST (Central GST)
What it is: Tax collected by Central Government (Ministry of Finance)
Applies to:
- Intrastate transactions (within same state)
- Goods/services supplied within the state
Rate structure:
- Products: 5%, 12%, 18%, 28%
- Services: Usually 18%
Example: Karnataka-based company sells to another Karnataka company
- CGST = 9% (of half the total GST rate for that category)
- SGST = 9% (Karnataka's state tax)
- Total GST = 18%
Who pays: Ultimately the end consumer; businesses collect and deposit
SGST (State GST)
What it is: Tax collected by State Government (State Excise Department)
Applies to:
- Intrastate transactions (within same state)
- Goods/services supplied within the state
Rate structure:
- Products: 5%, 12%, 18%, 28%
- Services: Usually 18%
Example: Maharashtra-based company sells to another Maharashtra company
- CGST = 9% (of the total GST rate)
- SGST = 9% (Maharashtra's state tax)
- Total GST = 18%
Who pays: Ultimately the end consumer; businesses collect and deposit
IGST (Integrated GST)
What it is: Tax on interstate and international transactions (combined central + state)
Applies to:
- Interstate transactions (seller and buyer in different states)
- Imports
- Services from foreign suppliers
Rate structure:
- Products: 5%, 12%, 18%, 28%
- Services: Usually 18%
Example: Karnataka company sells to Delhi company
- IGST = 18% (combined center + state)
- No separate CGST + SGST
- IGST goes to importing state's coffers
Who pays: Ultimately the end consumer; businesses collect and deposit
Quick Comparison Table
| Aspect | CGST | SGST | IGST |
|---|---|---|---|
| Applies to | Intrastate | Intrastate | Interstate/International |
| Collected by | Central Government | State Government | Central Government |
| Rate | 50% of total rate | 50% of total rate | 100% of total rate |
| Example | Karnataka to Karnataka | Maharashtra to Maharashtra | Karnataka to Delhi |
| Total Tax | CGST + SGST | CGST + SGST | IGST only |
How to Calculate Each Type
Example 1: Intrastate Transaction (CGST + SGST)
Scenario: Bangalore company sells goods to another Bangalore company
Transaction Details:
- Goods value: ₹10,000
- GST rate: 18% (applicable category)
Calculation:
CGST = Goods value × (18% ÷ 2) = ₹10,000 × 9% = ₹900
SGST = Goods value × (18% ÷ 2) = ₹10,000 × 9% = ₹900
Total GST = ₹900 + ₹900 = ₹1,800
Final Invoice Amount = ₹10,000 + ₹1,800 = ₹11,800
Breakdown:
- Seller deposits CGST: ₹900 to Central Government
- Seller deposits SGST: ₹900 to Karnataka State Government
- End customer pays: ₹11,800
Example 2: Interstate Transaction (IGST)
Scenario: Bangalore company sells goods to a Delhi company
Transaction Details:
- Goods value: ₹10,000
- GST rate: 18%
Calculation:
IGST = Goods value × 18% = ₹10,000 × 18% = ₹1,800
Final Invoice Amount = ₹10,000 + ₹1,800 = ₹11,800
Breakdown:
- Seller deposits IGST: ₹1,800 to Central Government
- Delhi receives its share later through settlement
- End customer pays: ₹11,800
Example 3: Service Transaction (Intrastate)
Scenario: Bangalore IT consultant provides services to Mumbai company
This is interstate (different states) so IGST applies.
Transaction Details:
- Service value: ₹50,000
- GST rate: 18% (standard for services)
Calculation:
IGST = ₹50,000 × 18% = ₹9,000
Final Invoice Amount = ₹50,000 + ₹9,000 = ₹59,000
Breakdown:
- Consultant deposits IGST: ₹9,000
- Mumbai company gets input credit (if registered)
- Effective cost: ₹50,000 (if they claim credit)
Input Tax Credit (ITC)
Crucial concept: GST system allows input tax credit.
If a registered business pays GST on purchases, they can deduct it from GST owed on sales.
Example:
- Manufacturing company buys raw materials: ₹1,00,000 + ₹18,000 GST = ₹1,18,000
- They sell finished goods: ₹2,00,000 + ₹36,000 GST = ₹2,36,000
- GST owed on sales: ₹36,000
- Less input tax credit: ₹18,000
- Net GST to pay: ₹18,000
Impact: Only the "value added" is taxed, not the entire value chain.
This is why businesses must maintain proper invoices and claim input credits.
GST Rates by Product Category
5% GST: Basic goods
- Food grains, fruits, vegetables
- Milk, eggs, fish, meat
- Books, newspapers
- Seeds
12% GST: Common goods and services
- Packaged food items
- Hotel rooms (non-AC)
- Passenger vehicles
18% GST: Most goods and services
- Branded goods
- Hotel services (AC rooms)
- IT services
- Financial services
- Professional services
28% GST: Luxury items
- Automobiles
- Cigarettes
- Aerated drinks
- Cosmetics
Determining Which GST Type Applies
Decision Tree:
Question 1: Are supplier and recipient in the same state?
- YES → Go to Question 2
- NO → Use IGST
Question 2: Is it an intrastate supply?
- YES → Use CGST + SGST
- NO (e.g., services) → Check location of recipient
Question 3: Is it an import?
- YES → Use IGST
- NO → Continue with above rules
Common Mistakes in GST Calculation
Mistake 1: Using CGST + SGST for Interstate Transactions
Wrong: Applying 9% CGST + 9% SGST to interstate transaction Right: Apply 18% IGST only
Mistake 2: Forgetting to Apply IGST to Services
Wrong: Thinking services only apply CGST + SGST Right: Services are also subject to IGST if interstate
Mistake 3: Not Claiming Input Tax Credit
Wrong: Not deducting GST paid on purchases Right: Claim ITC to reduce GST liability
Mistake 4: Mixing IGST with CGST/SGST
Wrong: Using CGST + SGST + IGST on same transaction Right: Either (CGST + SGST) OR IGST, never both
Mistake 5: Using Wrong GST Rate
Wrong: Applying 18% GST to a 5% product Right: Check classification and apply correct rate
Frequently Asked Questions
Q: Can unregistered businesses charge GST? A: No. Only GST-registered businesses can charge GST and claim ITC. If unregistered, you're outside GST system.
Q: What's the GST registration threshold? A: ₹40 lakhs annual turnover for goods, ₹20 lakhs for services (lower in certain states). Voluntary registration possible below threshold.
Q: Can I claim input credit on all purchases? A: No. Only on GST-paid supplies used for taxable supplies. Personal/exempt supplies don't qualify.
Q: How often do I file GST returns? A: Monthly (by 20th of next month) or quarterly. Depends on your registration type and turnover.
Q: What if I apply wrong GST type? A: You may face penalties, notice from GST authorities, and interest on unpaid tax. Correct immediately.
Q: How do I know if a supply is interstate or intrastate? A: Place of supply rules: For goods, it's the delivery location. For services, it's typically the recipient's location.
Q: Can GST rate change? A: Yes. GST Council can change rates. Check official GST rates before quoting to customers.
Q: What's HSN and SAC? A: HSN (for goods) and SAC (for services) are classification codes determining the GST rate. You must include them on invoices if applicable.
Q: Do I need separate bank accounts for CGST/SGST/IGST? A: No, not legally required. But maintaining clear records is essential for audits and returns.
Q: What if buyer is in different country? A: IGST applies plus potential additional import duties. Consult a customs broker for imports.
Calculate Your GST Correctly
Understanding IGST, CGST, and SGST is essential for any GST-registered business in India.
Use our sales tax calculator to:
- Calculate GST on any transaction
- Model different rate scenarios
- Understand tax impact on pricing
- Plan your business structure
Get GST calculations right from the start. It saves compliance headaches and tax penalties.
Also explore:
- Tax Bracket Calculator — Understand your income tax bracket
- Income Tax Calculator — Calculate your income tax liability
Sources & References
The figures, formulas, and guidance behind this GST Calculation Guide: IGST vs. CGST vs. SGST Explained draw on authoritative primary sources. For verification and further reading:
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