GST Calculator: How to Calculate GST on Any Amount (2025-26)
Whether you're a business owner raising an invoice, a consumer checking your bill, or a student learning about Indian taxation — knowing how to calculate GST is an essential skill. This guide explains the GST formula, all four tax slabs, CGST vs SGST vs IGST, and how to reverse-calculate GST from an inclusive price. Use our free GST calculator to get instant results.
What Is GST?
GST stands for Goods and Services Tax. It is a comprehensive, multi-stage, destination-based tax that was introduced in India on July 1, 2017, replacing a complex web of central and state taxes including VAT, service tax, excise duty, CST, and others.
GST is collected at every stage of the supply chain — from manufacturer to distributor to retailer — but the final tax burden falls on the end consumer. Businesses can claim a refund of GST paid on their purchases (called Input Tax Credit), ensuring that GST is effectively paid only on the value added at each stage.
India follows a dual GST model: the Centre and State governments both levy tax on goods and services. This is why you see CGST + SGST on most invoices.
The GST Formula: How to Add or Remove GST
Formula 1: Adding GST to a Price (Exclusive → Inclusive)
Use this when you know the base price and want to find the GST amount and total payable:
GST Amount = Original Price × GST Rate ÷ 100
Total (GST-inclusive) Price = Original Price + GST Amount
Formula 2: Removing GST from a Price (Inclusive → Exclusive)
Use this when the price you see already includes GST and you want to find the original base price:
Original Price = GST-inclusive Price × 100 ÷ (100 + GST Rate)
GST Amount = GST-inclusive Price − Original Price
This reverse calculation is especially useful when reading product MRPs or restaurant bills — in most cases the price shown is GST-inclusive.
Doing this manually is straightforward for round numbers, but for irregular amounts it's far easier to use our free GST calculator which handles both directions instantly.
GST Tax Slabs in India (2025-26)
India has four primary GST tax slabs, plus a zero-rate (exempt) category. Here's what falls under each:
| GST Rate | Category | Examples |
|---|---|---|
| 0% (Exempt) | Essential items, basic necessities | Fresh vegetables, milk, eggs, bread, salt, unbranded atta, healthcare services, education |
| 5% | Essential goods & basic services | Edible oil, sugar, spices, tea, coffee, economy air/train travel, life-saving drugs |
| 12% | Standard goods & services | Processed food, butter, ghee, smartphones, business class air travel, non-AC hotels |
| 18% | Most services & mid-range goods | Restaurants (AC), IT services, telecom, electronics, financial services, construction |
| 28% | Luxury & sin goods | Automobiles, large ACs, dishwashers, tobacco, cement, casinos, luxury hotels |
In addition to the 28% GST, some luxury and demerit goods also attract a Compensation Cess — for example, cigarettes and large cars carry an additional cess on top of 28% GST.
If you're unsure which GST rate applies to a specific product or service, you can look it up by its HSN code (Harmonized System of Nomenclature for goods) or SAC code (Services Accounting Code) on the GST portal.
CGST vs SGST vs IGST: What's the Difference?
Because India uses a dual GST structure, the tax is split differently depending on whether the transaction is within a state or across states.
| Tax Type | Full Form | When Applied | Who Gets Revenue |
|---|---|---|---|
| CGST | Central Goods & Services Tax | Intra-state transactions (buyer & seller in same state) | Central Government |
| SGST | State Goods & Services Tax | Intra-state transactions (buyer & seller in same state) | State Government |
| IGST | Integrated Goods & Services Tax | Inter-state transactions; imports | Central Govt (then distributed) |
How the Split Works in Practice
For any given GST rate, CGST and SGST are each exactly half:
- 5% GST intra-state = 2.5% CGST + 2.5% SGST
- 12% GST intra-state = 6% CGST + 6% SGST
- 18% GST intra-state = 9% CGST + 9% SGST
- 28% GST intra-state = 14% CGST + 14% SGST
For inter-state transactions, only IGST applies at the full rate (e.g., 18% IGST). This is why invoices from sellers in another state show IGST instead of CGST + SGST.
When filing returns, businesses reconcile ITC from IGST against CGST or SGST liabilities, and vice versa, according to prescribed rules.
Worked Examples: GST Calculations
Example 1: Adding 18% GST to a service invoice
A freelance developer charges ₹50,000 for a web project. The applicable GST rate is 18%.
- GST Amount = ₹50,000 × 18 ÷ 100 = ₹9,000
- Total Invoice = ₹50,000 + ₹9,000 = ₹59,000
- If intra-state: CGST = ₹4,500 + SGST = ₹4,500
Example 2: Removing 12% GST from a product MRP
A smartphone is priced at ₹22,400 (inclusive of 12% GST). What's the base price and GST?
- Original Price = ₹22,400 × 100 ÷ (100 + 12) = ₹22,400 ÷ 1.12 = ₹20,000
- GST Amount = ₹22,400 − ₹20,000 = ₹2,400
Example 3: Restaurant bill with 5% GST
Your total restaurant bill before tax is ₹1,800. The restaurant charges 5% GST (non-AC, no ITC).
- GST Amount = ₹1,800 × 5 ÷ 100 = ₹90
- Total Payable = ₹1,800 + ₹90 = ₹1,890
Example 4: Car with 28% GST + Cess
A mid-size SUV is priced at ₹12,00,000 (ex-showroom). GST is 28% + 17% cess = 45% effective.
- GST = ₹12,00,000 × 28 ÷ 100 = ₹3,36,000
- Cess = ₹12,00,000 × 17 ÷ 100 = ₹2,04,000
- Total Tax = ₹5,40,000
- On-road base = ₹17,40,000 (before RTO, insurance, etc.)
What Items Are Exempt from GST in India?
Several essential goods and services are fully exempt from GST (zero-rated or nil-rated). These include:
- Food staples: Fresh fruits, vegetables, milk, curd, lassi, eggs, bread, unbranded atta, salt, natural honey
- Healthcare: Medical services, hospitals, diagnostic services, life-saving drugs on the government's essential medicines list
- Education: School and university education, mid-day meal services
- Agricultural inputs: Seeds, fertilisers (many categories), agricultural equipment
- Financial services: Most banking and insurance services (though some are taxable)
- Religious services: Services by religious institutions
- Public transport: Metro rail, local train travel
Note that packaged or branded versions of the above (e.g., branded atta or packaged curd above a certain weight) may attract GST, even if the unbranded or loose version is exempt.
Input Tax Credit (ITC): What It Is and Why It Matters
One of the most powerful features of GST is the Input Tax Credit (ITC) mechanism. It allows registered businesses to deduct the GST they've paid on their purchases (inputs) from the GST they collect on their sales (output).
How ITC Works
Say you run a furniture business. You purchase raw wood for ₹1,00,000 and pay 12% GST = ₹12,000. You then sell the finished furniture for ₹2,00,000 and collect 12% GST = ₹24,000.
Without ITC, you'd pay ₹24,000 as GST. With ITC, you deduct the ₹12,000 already paid and remit only ₹12,000 to the government.
Why ITC Matters
- Eliminates the cascading "tax on tax" effect that existed pre-GST
- Lowers the effective cost of doing business for GST-registered entities
- Incentivises businesses to transact with registered vendors (to claim ITC)
- Consumers ultimately pay GST only on the final value-add, not on each stage's tax
ITC can only be claimed if the supplier has filed their GST returns and the purchase is used for business purposes. Certain items like personal use expenses, food for employees, and motor vehicles (in most cases) are not eligible for ITC.
Who Must Register for GST?
GST registration is mandatory if your annual turnover exceeds the threshold limits below:
| Category | General States | Special Category States* |
|---|---|---|
| Goods (supply) | ₹40 lakh/year | ₹20 lakh/year |
| Services | ₹20 lakh/year | ₹10 lakh/year |
| E-commerce sellers | Mandatory regardless of turnover | |
| Inter-state suppliers | Mandatory regardless of turnover | |
*Special category states: Manipur, Mizoram, Nagaland, Tripura, Arunachal Pradesh, Meghalaya, Sikkim, Himachal Pradesh, Uttarakhand, Jammu & Kashmir
Even if your turnover is below the threshold, voluntary GST registration can be beneficial — it allows you to claim ITC and issue tax invoices, which many B2B clients require.
GST vs Old Tax System: What Changed?
Before July 2017, India had a fragmented indirect tax system with multiple overlapping levies:
| Aspect | Pre-GST (Before 2017) | Post-GST (After 2017) |
|---|---|---|
| Number of taxes | 15+ central & state taxes (VAT, service tax, excise, CST…) | One unified GST (CGST + SGST/IGST) |
| Tax on tax (cascading) | Yes — taxes were levied on taxes | No — ITC eliminates cascading |
| Across-state trade | Complex, different rates per state | Unified IGST, seamless credit |
| Compliance | Multiple registrations, filings | Single registration, GSTN portal |
| Transparency | Low — hidden taxes in prices | High — tax shown separately on invoices |
GST significantly simplified compliance for most businesses, particularly those operating across multiple states. While implementation had initial challenges, the system has matured considerably and GST collections now regularly cross ₹1.7 lakh crore per month.
Frequently Asked Questions
How do I calculate GST on an amount?
To add GST: multiply the original price by the GST rate and divide by 100. Add the result to the original price. For example, ₹1,000 at 18% GST = ₹1,000 × 18/100 = ₹180 GST → total ₹1,180. Use our GST calculator to do this instantly.
How do I remove GST from a GST-inclusive price?
Divide the GST-inclusive price by (1 + GST rate/100). For example, ₹1,180 at 18% GST → ₹1,180 ÷ 1.18 = ₹1,000 original price; GST = ₹180.
What are the GST slabs in India?
India has four main GST slabs: 5% (essential goods), 12% (processed foods, smartphones), 18% (most services, electronics, restaurants), and 28% (luxury goods, automobiles). Many essential items are exempt at 0%.
What is the difference between CGST, SGST, and IGST?
CGST and SGST are levied on intra-state transactions — each at half the total GST rate (e.g., 9% CGST + 9% SGST for 18% GST). IGST is levied on inter-state transactions at the full GST rate.
Is GST calculated on MRP or selling price?
GST is calculated on the transaction value (selling price). For most retail products, the MRP displayed on packaging is already GST-inclusive — the seller has factored in GST when printing the MRP.
What items are exempt from GST in India?
Exempt items include fresh produce (vegetables, fruits, milk, eggs), bread, salt, unbranded flour, education services, hospital and healthcare services, and most banking services.
What is Input Tax Credit (ITC) in GST?
ITC lets GST-registered businesses deduct the GST they paid on their purchases from the GST they collected on sales. This prevents tax-on-tax cascading and lowers the effective tax burden for businesses.
Who needs to register for GST?
Businesses with annual turnover above ₹40 lakh (goods) or ₹20 lakh (services) in general states must register for GST. E-commerce sellers and inter-state suppliers must register regardless of turnover.
How is GST different from the old tax system?
GST replaced 15+ central and state taxes (VAT, service tax, excise, CST, etc.) with a single unified tax. It eliminated cascading taxes, unified state markets, and simplified multi-state compliance significantly.
Can I use DoItSwift's GST calculator for free?
Yes — our GST calculator is completely free. Enter an amount and select a GST rate to instantly calculate GST payable or reverse-calculate the original price from a GST-inclusive amount.
Calculate GST in Seconds
No sign-up. No ads. No data sent to servers. Just fast, accurate GST calculations.