GST Calculator
Add GST to a base amount or strip it out of an inclusive price — any slab, with the CGST/SGST split and grand total.
What is Goods and Services Tax (GST)?
Goods and Services Tax (GST) is India's comprehensive, destination-based indirect tax levied on the manufacture, sale, and consumption of goods and services across the country. Enacted under the Constitution (101st Amendment) Act, GST subsumed numerous legacy central and state levies—including Central Excise Duty, Service Tax, State VAT, Entry Tax, and Luxury Tax—into a unified tax architecture.
GST is structured under four statutory tiers: Central GST (CGST) and State GST (SGST) (or Union Territory GST) levied equally on intra-state supplies, and Integrated GST (IGST) levied on inter-state commerce and international imports. This calculator functions in two operational directions: adding tax to a base amount (Exclusive mode) or extracting base value and tax components from a gross invoice price (Inclusive mode).
Forward vs Reverse GST Calculation Mechanics
Commercial invoicing requires two standard mathematical procedures depending on pricing agreements:
- GST Exclusive (Forward Calculation): Applied when a quote or contract states prices net of taxes. The applicable GST percentage is multiplied by the base price and added to derive the final payable invoice total.
- GST Inclusive (Reverse Calculation / Tax Extraction): Applied when consumer retail prices or lump-sum contracts are quoted as "inclusive of all taxes". Here, the base pre-tax value is extracted by dividing the total price by $(1 + r div 100)$, and the tax content is the difference.
The GST Mathematical Formulas
Exclusive: GST = Base × (r ÷ 100) | Inclusive: Base = Total ÷ (1 + r ÷ 100)
- Base: Net price before indirect taxation
- r: Notified statutory GST rate percentage (0.25%, 3%, 5%, 12%, 18%, or 28%)
- GST Amount: In Exclusive mode: Base × (r ÷ 100); In Inclusive mode: Total − Base
- CGST & SGST Split: On intra-state sales, GST divides equally: CGST = GST ÷ 2, and SGST = GST ÷ 2
- IGST: On inter-state transactions, full GST applies as IGST without split
Worked example: Exclusive & Inclusive GST Math on 18%
Scenario A — Adding 18% GST to ₹1,00,000 Base Amount:
- Base Amount: ₹1,00,000
- GST at 18%: ₹1,00,000 × (18 ÷ 100) = ₹18,000
- CGST (9%): ₹9,000 | SGST (9%): ₹9,000 (or IGST ₹18,000)
- Total Invoice Amount: ₹1,00,000 + ₹18,000 = ₹1,18,000
Scenario B — Extracting GST from ₹1,18,000 Inclusive Price:
- Total Gross Price: ₹1,18,000
- Base Pre-tax Value: ₹1,18,000 ÷ (1 + 0.18) = ₹1,00,000
- Embedded GST: ₹1,18,000 − ₹1,00,000 = ₹18,000
Standard GST Slabs and Scheduled Commodity Profiles
| GST Rate | Statutory Classification | Sample Goods & Services | Tax on ₹1,00,000 Base |
|---|---|---|---|
| 0.25% | Special Low Rate | Rough diamonds, unworked precious stones | ₹250 |
| 3% | Precious Metals | Gold, silver, platinum jewellery | ₹3,000 |
| 5% | Household Essentials | Packaged food grains, edible oil, footwear <₹1,000, rail tickets | ₹5,000 |
| 12% | Standard Low Rate | Processed dairy, apparel >₹1,000, business class air tickets | ₹12,000 |
| 18% | Standard Service Rate | Software, IT consulting, telecom, banking, consumer electronics | ₹18,000 |
| 28% | Luxury & Sin Rate | Motor cars, aerated beverages, tobacco, air conditioners | ₹28,000 |
Input Tax Credit (ITC) Flow and Invoice Matching
The defining strength of the GST regime is the seamless flow of Input Tax Credit (ITC). When a registered business purchases goods or services for business use, the GST paid on purchases (Input Tax) can be offset directly against the GST collected on sales (Output Tax), preventing cascading taxation ("tax on tax").
To claim ITC legally under Section 16 of the CGST Act, four statutory conditions must be satisfied: (1) Possession of a valid GST tax invoice, (2) Actual receipt of goods or services, (3) Supplier must have filed Form GSTR-1 and the credit must appear in the buyer's Form GSTR-2B, and (4) The supplier must have remitted the tax to the government.
Reverse Charge Mechanism (RCM) Provisions
Under regular GST billing, the supplier collects tax from the buyer and deposits it with the government. Under the Reverse Charge Mechanism (RCM) under Section 9(3) and 9(4), statutory liability to remit GST directly to the government shifts to the recipient.
Common commercial supplies subject to mandatory RCM include: legal services provided by advocates, goods transport agency (GTA) services, sponsorship services, and services provided by directors to a company. Tax paid under RCM is eligible for ITC if used for business furtherance.
Frequently Asked Questions on GST
Key insights into rate slabs, inclusive tax extraction, input tax credit, and business thresholds.
Divide the gross inclusive price by (1 + GST rate as a decimal). For example, at an 18% GST slab, divide the gross bill by 1.18 to determine the base pre-tax value. Subtracting this base amount from the gross price gives the exact GST amount included in the bill.
CGST (Central GST) and SGST (State GST) apply concurrently on transactions taking place within the same state (intra-state), with the tax split equally between the Central and State governments. IGST (Integrated GST) applies on transactions between two different states (inter-state) or imports, collected by the Centre and apportioned to the consuming state.
The 18% slab is the most widely applied rate, covering most commercial services (IT software, banking, financial services, telecom, consulting, hospitality) and manufactured items such as capital machinery, electronic accessories, and branded consumer packaged goods.
ITC allows businesses to deduct the GST they paid on business purchases (raw materials, capital assets, professional services) from the GST they collect on sales. For instance, if you collect ₹50,000 GST on sales and paid ₹30,000 on inputs, you only remit ₹20,000 net cash to the government.
Fresh unbranded agricultural produce (fruits, vegetables, milk, eggs), healthcare services by clinical establishments, and educational services are completely exempt. Additionally, alcoholic liquor for human consumption and five specified petroleum products (crude oil, petrol, diesel, aviation fuel, natural gas) remain outside GST and continue to attract State VAT and Central Excise.
For suppliers of goods, registration is mandatory if annual aggregate turnover exceeds ₹40 lakh (₹20 lakh in special category states). For service providers, the mandatory threshold is ₹20 lakh (₹10 lakh in special category states). Any business engaged in inter-state taxable supply must register irrespective of turnover.
No. Unregistered end-consumers cannot claim Input Tax Credit; the GST charged on retail goods and services forms a final, non-refundable part of their total purchase expense.
RCM is a statutory mechanism where the recipient of goods or services is liable to pay GST directly to the government instead of the supplier. This applies to specified notified supplies such as advocate legal services, GTA transport services, and director remuneration.
The Composition Scheme is a simplified compliance option for small businesses with turnover up to ₹1.5 crore (₹75 lakh for services/restaurants). Composition dealers pay a low turnover tax (1% for manufacturers/traders, 5% for restaurants, 6% for service providers), cannot issue tax invoices, cannot collect GST from customers, and cannot claim ITC.
An e-Way Bill is an electronic document generated on the GST portal for consignments of goods exceeding ₹50,000 in value moving between locations. It tracks the physical movement of goods and verifies that applicable GST has been accounted for by the consignor or transporter.