GST Calculator 2025-26: How to Calculate GST (Formula, Examples & Free Tool)

Every Indian business — from a kirana store in Dadar to a manufacturing unit in Bhiwandi — needs to calculate GST accurately on every transaction. Getting the GST calculation wrong means either overcharging your customers or under-reporting tax, both of which create compliance problems. This guide explains the GST calculation formulas for all scenarios, walks through real examples, and gives you a free tool to calculate instantly.

Skip the formulas? Use our free GST Calculator to calculate CGST, SGST, and IGST instantly for any amount and rate.

Understanding GST: The Basics

Goods and Services Tax (GST) is India's unified indirect tax that replaced multiple taxes like VAT, Service Tax, and Excise Duty. GST has three components:

• CGST (Central GST): Collected by the Central Government on intra-state supplies
• SGST (State GST): Collected by the State Government on intra-state supplies
• IGST (Integrated GST): Collected by the Central Government on inter-state supplies and imports

For intra-state transactions (e.g., selling goods within Maharashtra), the GST rate is split equally between CGST and SGST. For inter-state transactions (e.g., selling from Maharashtra to Gujarat), the full rate applies as IGST.

Current GST Rate Slabs

Need to find the correct HSN code and GST rate for your product? Use our [HSN Code Finder](/tools/hsn-code-finder.html) with 21,000+ codes.

GST Calculation Formulas

There are two common scenarios: calculating GST on top of a base price (exclusive) and extracting GST from a price that already includes tax (inclusive).

Formula 1: GST Exclusive (Adding GST to Base Price)

When you know the base price and need to calculate the total price including GST:

GST Amount = Base Price × (GST Rate / 100)

Total Price = Base Price + GST Amount

For intra-state (CGST + SGST):

CGST = Base Price × (GST Rate / 200)

SGST = Base Price × (GST Rate / 200)

Total = Base Price + CGST + SGST

For inter-state (IGST):

IGST = Base Price × (GST Rate / 100)

Total = Base Price + IGST

Formula 2: GST Inclusive (Extracting GST from Total Price)

When you have a price that already includes GST and need to find the base price:

Base Price = Total Price × (100 / (100 + GST Rate))

GST Amount = Total Price − Base Price

Extract GST from inclusive prices instantly with our [Reverse GST Calculator](/tools/reverse-gst-calculator.html).

GST Calculation Examples

Let's work through practical examples that Mumbai business owners encounter daily.

Example 1: Intra-State Sale (Within Maharashtra) at 18% GST

Scenario: You sell IT services to a client in Pune for ₹1,00,000 (base price). Your business is in Mumbai.

Both buyer and seller are in Maharashtra → Intra-state → CGST + SGST applies.

Example 2: Inter-State Sale (Maharashtra to Gujarat) at 18% GST

Scenario: You sell the same IT services to a client in Ahmedabad for ₹1,00,000.

Seller in Maharashtra, buyer in Gujarat → Inter-state → IGST applies.

Note: The total is the same (₹1,18,000), but the tax component allocation differs — important for correct GST return filing.

Example 3: GST Inclusive Price Calculation

Scenario: A product is listed at ₹5,900 (inclusive of 18% GST). What is the base price?

Base Price = ₹5,900 × (100 / 118) = ₹5,000

GST Amount = ₹5,900 − ₹5,000 = ₹900

CGST = ₹450 | SGST = ₹450 (if intra-state)

Example 4: Multiple Items at Different GST Rates

Scenario: You're creating an invoice with:

• Item A: ₹10,000 @ 5% GST
• Item B: ₹25,000 @ 18% GST
• Item C: ₹5,000 @ 28% GST

Create GST-compliant invoices with automatic calculations using our free [Invoice Generator](/tools/invoice-generator.html).

GST Calculation in Tally Prime

Tally Prime automates GST calculations, but understanding the setup ensures accuracy:

Setting Up GST in Tally Prime

1. Enable GST: Gateway → F11 → Enable Goods and Services Tax (GST)
2. Set GSTIN: Enter your GST registration number (validate it first with our GSTIN Validator)
3. Configure Tax Rates: Set HSN/SAC codes and applicable rates for each stock item or service
4. Place of Supply: Tally auto-determines CGST/SGST vs IGST based on party state codes
5. Record Sales/Purchases: GST is calculated automatically based on configured rates

GST Reports in Tally Prime

Tally Prime generates all GST reports you need:

• GSTR-1 — Outward supplies report
• GSTR-3B — Summary return with tax liability
• GSTR-2A/2B Reconciliation — Match your purchases with supplier data
• GST Computation — Period-wise tax liability summary
• HSN-wise Summary — Required for filing

As a Tally 5-Star Certified Partner, Mark IT Solutions can configure GST settings in your Tally Prime for accurate automated calculations. Contact us for setup assistance.

Input Tax Credit (ITC) and GST Calculation

Understanding ITC is essential for calculating your net GST liability:

Net GST Payable = Output GST (collected on sales) − Input GST (paid on purchases)

Example:

• GST collected on sales (output): ₹50,000
• GST paid on purchases (input): ₹35,000
• Net GST payable: ₹50,000 − ₹35,000 = ₹15,000

ITC Conditions

To claim ITC, ensure:

1. You have a valid tax invoice from the supplier
2. The goods/services have been received
3. The supplier has filed their return and the tax is visible in your GSTR-2B
4. You have paid the supplier within 180 days
5. Your GSTIN is active and not suspended

Paid GST late? Calculate your interest liability with our [GST Interest Calculator](/tools/gst-interest-calculator.html).

GST Late Fee and Interest

Missing GST payment deadlines attracts both late fees and interest:

Interest on Late GST Payment

• 18% per annum on the net tax liability (after adjusting ITC)
• Calculated from the day after the due date to the actual payment date

Late Filing Fees

• GSTR-1: ₹50/day (₹20/day for nil return), max ₹5,000
• GSTR-3B: ₹50/day (₹20/day for nil return), max ₹5,000
• GSTR-9 (Annual): ₹200/day (₹100 CGST + ₹100 SGST), max 0.25% of turnover

Calculate your exact late fee and interest with our [GST Late Fee Calculator](/tools/gst-late-fee-calculator.html).

GST for Different Business Types in Mumbai

Traders and Retailers

• Most goods attract 5%, 12%, or 18% GST
• Calculate GST on the selling price (exclusive basis)
• Claim ITC on all business purchases
• Use HSN Code Finder for accurate classification

Service Providers (IT, Professional, Consulting)

• Most services attract 18% GST
• Inter-state services attract IGST
• Export of services is zero-rated (with refund of ITC)
• SAC codes apply instead of HSN codes

Manufacturers

• GST on finished goods at applicable rate
• Full ITC on raw materials, capital goods, and input services
• E-invoicing mandatory if turnover exceeds ₹5 Crore (check with our E-Invoice Eligibility Checker)

Restaurants and Food Businesses

• Restaurants without AC: 5% (no ITC)
• Restaurants with AC: 5% (no ITC)
• Outdoor catering: 18% (with ITC in some cases)
• Cloud kitchens: 5% (treated as restaurant service)