📋 In This Page
- What is GST and why it matters for every Indian business
- GST formula — how to add and remove GST step by step
- GST slab rates — complete list of goods and services
- CGST vs SGST vs IGST — key differences explained
- Real-world GST calculation examples (India, 2026)
- 5 common GST calculation mistakes to avoid
- Frequently asked questions
What is GST and Why It Matters for Every Indian Business
Goods and Services Tax (GST) is India's unified indirect tax, introduced on 1 July 2017 to replace a complex web of Central Excise, Service Tax, VAT, and over a dozen other levies. It is a destination-based, multi-stage tax collected at every point of value addition — but ultimately borne only by the final consumer, thanks to the Input Tax Credit (ITC) mechanism.
For businesses, freelancers, and consumers in India, GST affects nearly every transaction. A freelance developer billing a client, a manufacturer buying raw materials, a restaurant charging a customer, a car dealer selling a vehicle — all involve GST calculations. Getting the arithmetic right has direct consequences: overcharging a customer by even ₹1 is technically an offence; undercharging means the shortfall comes out of your margin.
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Manufacturers & Traders
Calculate tax on every input purchase and output sale. Claim ITC to avoid paying GST twice on the same goods.
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Freelancers & Services
If your annual turnover exceeds ₹20 lakh (₹10 lakh in some states), GST registration is mandatory and you must charge 18% on invoices.
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Consumers
Understand what portion of your bill is actual price vs. tax. Helps verify restaurant bills, e-commerce invoices, and service quotations.
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Accountants & Finance Teams
Reconcile GST returns (GSTR-1, GSTR-3B), split CGST/SGST/IGST correctly, and ensure compliance with filing deadlines.
GST registration threshold (2026): Businesses with annual aggregate turnover above ₹40 lakh (goods) or ₹20 lakh (services) in most states must mandatorily register under GST. Threshold is ₹20 lakh for goods and ₹10 lakh for services in the special category states (north-eastern and hill states).
GST Formula — How to Add and Remove GST Step by Step
There are two common scenarios in every GST calculation. The first is adding GST to a base (exclusive) price to arrive at the final invoice amount. The second is reverse-extracting GST from an inclusive price — which is far more commonly done wrong.
Formula 1 — Adding GST to a base price
Add GST (Exclusive Price → Inclusive Price)
GST Amount = Base Price × (GST Rate ÷ 100)
Total Price = Base Price + GST Amount
CGST = SGST = GST Amount ÷ 2 (intra-state)
IGST = GST Amount (inter-state)
Total Price = Base Price + GST Amount
CGST = SGST = GST Amount ÷ 2 (intra-state)
IGST = GST Amount (inter-state)
Formula 2 — Removing GST from an inclusive price
Remove GST (Inclusive Price → Base Price)
Base Price = Total Price ÷ (1 + GST Rate ÷ 100)
GST Amount = Total Price − Base Price
OR: GST Amount = Total Price × (GST Rate ÷ (100 + GST Rate))
GST Amount = Total Price − Base Price
OR: GST Amount = Total Price × (GST Rate ÷ (100 + GST Rate))
⚠️
The most common mistake when removing GST is calculating Total × (GST% ÷ 100) — this gives you the wrong number. For an ₹11,800 inclusive amount at 18%, this formula gives ₹2,124 (wrong). The correct GST is ₹1,800. Always use the reverse formula above.
Worked example — IT services invoice
Example: IT consulting invoice of ₹50,000 base amount at 18% GST (intra-state, e.g. both parties in Maharashtra)
Base Amount: ₹50,000
GST Rate: 18%
GST Amount: ₹50,000 × 0.18 = ₹9,000
CGST (9%): ₹50,000 × 0.09 = ₹4,500
SGST (9%): ₹50,000 × 0.09 = ₹4,500
Total Invoice Amount = ₹50,000 + ₹9,000 = ₹59,000 ✓
Worked example — Reverse calculation from restaurant bill
Example: Restaurant bill of ₹2,360 (GST-inclusive) at 5% GST — what is the base food cost?
Inclusive Amount: ₹2,360
GST Rate: 5%
Base Price = ₹2,360 ÷ 1.05 = ₹2,247.62
GST Amount = ₹2,360 − ₹2,247.62 = ₹112.38
CGST (2.5%) = ₹56.19 | SGST (2.5%) = ₹56.19
Food Cost = ₹2,247.62 + GST ₹112.38 = Total ₹2,360 ✓
GST Slab Rates — Complete List of Common Goods and Services (2026)
India's GST structure has four primary tax slabs — 5%, 12%, 18%, and 28% — plus a 0% exempt category for essential items. A few special rates (0.25%, 3%) apply to precious stones and metals. Below is a practical reference table for the most commonly transacted categories.
| Category | GST Rate | Examples | Transaction Type |
|---|---|---|---|
| Fresh produce, milk, eggs | 0% — Exempt | Vegetables, milk, rice (unbranded), flour | Goods |
| Gold, silver, platinum | 3% | Jewellery, bullion, coins | Goods |
| Essential services & goods | 5% | Railways, economy flights, life-saving drugs, edible oil | Both |
| Processed & packaged food | 12% | Butter, ghee, cheese, packaged namkeen, fruit juices | Goods |
| Consumer electronics | 12% | Mobile phones, laptops, tablets (phones above ₹12,000 → 18%) | Goods |
| IT, telecom, financial services | 18% | Software, cloud, internet plans, insurance, CA fees | Services |
| Restaurants (AC / non-AC) | 5% / 18% | 5% for standalone restaurants; 18% in 5-star hotels | Services |
| Construction services | 5–18% | 5% (affordable housing); 12% (commercial); 18% (premium) | Services |
| Automobiles — small cars | 28% + 1% cess | Petrol engine below 1200cc, diesel below 1500cc | Goods |
| Automobiles — large SUVs | 28% + 22% cess | Engine above 1500cc, length above 4m | Goods |
| Tobacco & aerated drinks | 28% + cess | Cigarettes, pan masala, soft drinks | Goods |
| Electric vehicles | 5% | EVs of all types (reduced from 12% in 2019) | Goods |
💡GST rates are assigned based on HSN (Harmonized System of Nomenclature) codes for goods and SAC (Services Accounting Code) for services. When in doubt, look up the exact HSN/SAC code for your product or service on the official GST portal at gstn.gov.in before raising an invoice.
CGST vs SGST vs IGST — Key Differences Explained
One of the most confusing aspects of GST for new business owners is understanding the three components — CGST, SGST, and IGST — and knowing which applies to a given transaction. The rule is straightforward once you understand the logic.
| Component | Full Form | When Applied | Rate (example: 18% GST) | Revenue Goes To |
|---|---|---|---|---|
| CGST | Central Goods & Services Tax | Intra-state transactions | 9% (half of 18%) | Central Government |
| SGST | State Goods & Services Tax | Intra-state transactions | 9% (half of 18%) | State Government |
| IGST | Integrated Goods & Services Tax | Inter-state & imports | 18% (full rate) | Central Govt (distributed later) |
| UTGST | Union Territory GST | Intra-UT transactions | 9% (same as SGST) | Union Territory |
Practical rule — when to use which
- Supplier and buyer are in the same state: Charge CGST + SGST (each at half the GST rate)
- Supplier and buyer are in different states: Charge IGST (at the full GST rate)
- Imports into India: IGST applies (treated as inter-state supply)
- Exports from India: Zero-rated (0% IGST, but ITC refund available)
Why it matters for ITC claims: CGST paid can only be used to offset CGST liability. SGST can only offset SGST. IGST can offset IGST first, then CGST, then SGST — in that order. Getting the tax type wrong on your invoice can block input tax credit for your buyer, leading to disputes and penalties.
| Transaction Example | Supplier State | Buyer State | Tax Applied |
|---|---|---|---|
| IT services invoice | Karnataka | Karnataka | CGST 9% + SGST 9% |
| Goods shipment | Maharashtra | Delhi | IGST 18% |
| Import of machinery | Overseas | Tamil Nadu | IGST (at applicable rate) |
| Software export | Hyderabad | USA | Zero-rated (0% IGST) |
| Restaurant bill (AC, Delhi) | Delhi | Delhi customer | CGST 2.5% + SGST 2.5% |
Real-World GST Calculation Examples (India, 2026)
These examples cover the most common situations where Indian businesses and individuals need to calculate GST — from freelance invoices to car purchases to restaurant bills. Use the calculator above with these inputs to verify the results instantly.
| Scenario | Base Amount | GST Rate | GST Amount | Total (incl. GST) | CGST / SGST |
|---|---|---|---|---|---|
| Freelance design invoice | ₹25,000 | 18% | ₹4,500 | ₹29,500 | ₹2,250 each |
| Mobile phone purchase | ₹15,000 | 18% | ₹2,700 | ₹17,700 | ₹1,350 each |
| Restaurant bill (AC) | ₹2,000 | 5% | ₹100 | ₹2,100 | ₹50 each |
| Gold jewellery (50g) | ₹2,50,000 | 3% | ₹7,500 | ₹2,57,500 | ₹3,750 each |
| CA firm annual retainer | ₹1,20,000 | 18% | ₹21,600 | ₹1,41,600 | ₹10,800 each |
| Hatchback car (1000cc) | ₹6,50,000 | 29% (28%+1%) | ₹1,88,500 | ₹8,38,500 | IGST if inter-state |
| Electric scooter | ₹85,000 | 5% | ₹4,250 | ₹89,250 | ₹2,125 each |
| Internet plan (annual) | ₹6,000 | 18% | ₹1,080 | ₹7,080 | ₹540 each |
💡Click any row's values into the calculator above to verify. The slight differences you may see for goods like cars arise from additional cess components which are calculated separately from the base GST and are not included in the standard CGST/SGST split.
5 Common GST Calculation Mistakes to Avoid
These are the most frequent errors Indian businesses and freelancers make when calculating or applying GST — each with real financial or compliance consequences. Avoiding these will save you from penalties, ITC mismatches, and invoice disputes.
Mistake 1 — Using the wrong reverse formula
✗ Wrong: GST in ₹11,800 at 18% = ₹11,800 × 18% = ₹2,124
✓ Right: GST = ₹11,800 × 18 ÷ (100 + 18) = ₹11,800 × 18/118 = ₹1,800
Multiplying an inclusive price by the GST percentage gives an inflated and incorrect GST amount. The correct reverse formula divides the rate by (100 + rate). This mistake leads to incorrect ITC claims and invoice reconciliation failures during GST audits. Use the "Remove GST" mode of this calculator to avoid this completely.
Mistake 2 — Applying IGST on an intra-state transaction
✗ Wrong: Supplier and buyer both in Mumbai — charging 18% IGST on invoice
✓ Right: Same-state transaction = 9% CGST + 9% SGST on the invoice
Charging IGST on an intra-state supply is a fundamental classification error. The buyer cannot claim CGST/SGST ITC against IGST charged incorrectly. This creates cascading tax issues. The GST portal will flag the mismatch between your GSTR-1 and the buyer's GSTR-2A, triggering notices from the department.
Mistake 3 — Applying the wrong GST rate for the product/service
✗ Wrong: Charging 18% GST on gold jewellery (actual rate: 3%)
✓ Right: Always look up the exact HSN/SAC code on the GST portal before invoicing
GST rates are HSN-code specific, not industry-category specific. Two similar-sounding products can have very different rates. For example, branded snacks and unbranded snacks attract different rates. When in doubt, search the product's HSN code on the official GSTN portal or CBIC's rate finder. Overcharging GST is an offence; undercharging means you absorb the liability.
Mistake 4 — Not including GST in the invoice base for composition dealers
✗ Wrong: Composition dealer charging GST separately on the invoice like a regular dealer
✓ Right: Composition dealers cannot charge GST separately — they pay it from their own pocket on a flat turnover basis
Businesses registered under the GST Composition Scheme (turnover below ₹1.5 crore for goods, ₹50 lakh for services) cannot issue tax invoices or charge GST from customers. They pay a flat composition tax rate (1%–6% depending on type) from their margin. Charging GST separately on a composition dealer invoice is illegal and can lead to cancellation of the composition registration.
Mistake 5 — Ignoring GST on advances received
✗ Wrong: Receiving a ₹1,00,000 advance for a future project and not accounting for GST on it
✓ Right: GST is applicable on advances received for services (not goods, post Jan 2018 amendment)
Under GST rules, when an advance is received for a supply of services, GST must be paid on that advance even before the service is delivered. Failing to account for GST on advance receipts leads to mismatches in GSTR-1 and GSTR-3B, attracts interest at 18% per annum on the shortfall, and can lead to scrutiny notices. Note that since January 2018, this rule no longer applies to advance payments for supply of goods.
🧾 Calculate GST on Any Amount — Instantly Free
Use the free GST calculator above for invoicing, ITC calculations, quotations, or just to verify your bills. Covers all slabs, CGST/SGST/IGST split, and reverse calculation. No signup, no ads.
Calculate GST Now →Frequently Asked Questions
To add GST to a base price, multiply the base price by the GST rate divided by 100 to get the GST amount, then add it to the base price. For example, ₹10,000 at 18% GST: the GST amount is ₹1,800 and the total is ₹11,800. For intra-state transactions, CGST and SGST are each half of the GST rate (9% each at 18%). For inter-state, IGST at the full 18% applies. Use the calculator above for an instant, error-free result with a full breakdown.
The reverse GST formula is: Base Price = Total Price ÷ (1 + GST Rate ÷ 100). The GST amount equals the total price minus the base price. The common mistake is calculating Total Price × GST% which gives the wrong answer. For ₹11,800 inclusive of 18% GST: Base = ₹11,800 ÷ 1.18 = ₹10,000. GST = ₹1,800. Use the "Remove GST" mode in the calculator above to get the correct reverse calculation instantly.
CGST (Central GST) and SGST (State GST) are both charged on intra-state transactions — when the supplier and buyer are in the same state. Each is exactly half the total GST rate. So at 18% total GST, you pay 9% CGST to the central government and 9% SGST to the state government. IGST (Integrated GST) is charged at the full rate on inter-state transactions — when goods or services cross state borders. IGST is initially collected by the central government and then distributed to the destination state. Always check whether your transaction is intra or inter-state before raising an invoice.
India has four primary GST slabs: 5% for essential goods and services like unbranded food, public transport, and certain medicines; 12% for processed food items, butter, and mobile phones; 18% for the majority of services including IT, telecom, financial services, and restaurants; 28% for luxury and sin goods like cars, tobacco, aerated drinks, and premium hotels. Additionally, fresh produce, milk, and basic necessities are entirely exempt (0%). Special rates of 3% apply to gold and silver, and 0.25% to rough precious stones. The GST Council periodically reviews and revises these rates.
Yes, most services in India attract 18% GST. This includes IT and software services, telecom, financial advisory, insurance, legal and CA services, restaurants, event management, and most professional services. Some services are exempt from GST — notably healthcare, education, and certain government services. A few services attract 5% (like economy-class air travel) or 12% (like business-class air travel). Every service is assigned a SAC (Services Accounting Code), and the GST rate is determined by that code. Freelancers and service businesses with turnover exceeding ₹20 lakh per year must register for GST and charge it on their invoices.
The GST rate on restaurant food depends on the type of establishment. Standalone restaurants — both air-conditioned and non-air-conditioned — attract 5% GST, but without the ability to claim input tax credit. Restaurants located within hotels where room tariff is above ₹7,500 per night attract 18% GST (with ITC). Outdoor catering services attract 18% GST. Packaged food bought from a grocery store attracts 5% or 12% GST depending on whether it is branded. Food ordered from cloud kitchens via apps like Swiggy or Zomato attracts the same rate as the supplying restaurant — typically 5%.
New cars attract a base GST of 28% plus an additional cess that varies by engine size and fuel type. Small petrol cars with engine capacity below 1200cc attract 28% GST + 1% cess = 29% total. Small diesel cars below 1500cc attract 28% + 3% cess = 31%. Mid-size cars attract 28% + 15% cess. Large sedans and SUVs with engines above 1500cc attract 28% + 20–22% cess = up to 50% total. Electric vehicles are a significant exception — they attract only 5% GST with no cess, making them considerably cheaper from a tax perspective than comparable petrol or diesel vehicles.
No, exports are zero-rated under GST — meaning the effective GST rate is 0% on exported goods and services. This is different from being exempt: zero-rated means the exporter can still claim a full refund of any input GST paid on materials or services used to produce the exported product. This mechanism prevents Indian exports from carrying an embedded tax cost, keeping them competitive internationally. To claim the refund, exporters must file a Letter of Undertaking (LUT) or pay IGST on exports and then claim a refund through the GST portal.
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