Blog  /  27 May 2026

How to Calculate GST on Invoice — CGST, SGST and IGST Explained

GST calculation confuses many small business owners — not because it is difficult, but because the terminology (CGST, SGST, IGST, inclusive, exclusive) sounds more complicated than it is. This guide explains GST calculation in plain language with examples you can apply immediately.

The Three Types of GST in India

India's GST system has three components, and which one applies depends on where you and your customer are located:

• CGST (Central GST): Collected by the Central Government. Applies on intrastate (within same state) transactions. Rate is half of the total GST rate.
• SGST (State GST): Collected by the State Government. Also applies on intrastate transactions. Rate is the other half of the total GST rate.
• IGST (Integrated GST): Applies on interstate (between different states) transactions. Rate is the full GST rate. Collected by the Central Government, then distributed to the destination state.

For most small shops serving local customers, intrastate transactions are the norm — so CGST + SGST is what you will deal with day to day. Interstate transactions (selling to buyers in another state) attract IGST.

GST-Exclusive Calculation (Adding GST on Top of the Price)

This is the most common scenario — your product price does not include GST, and you add GST on top for the invoice.

Example: You sell a product at ₹1,000 (before GST) with 18% GST.

• GST Amount = ₹1,000 × 18% = ₹180
• CGST (9%) = ₹90 | SGST (9%) = ₹90
• Total Invoice = ₹1,000 + ₹180 = ₹1,180

Use the free GST Calculator to verify calculations instantly for any amount and rate.

GST-Inclusive Calculation (Extracting GST from an All-Inclusive Price)

Sometimes the selling price already includes GST — common in retail where you display MRP (which is GST-inclusive). You need to extract the base price and GST amount from the all-inclusive price.

Example: A product's MRP is ₹1,180 inclusive of 18% GST.

• Base Price = ₹1,180 × 100 / 118 = ₹1,000
• GST Amount = ₹1,180 − ₹1,000 = ₹180
• CGST (9%) = ₹90 | SGST (9%) = ₹90

GST Rates in India — Quick Reference

GST in India is levied at five main rates. The rate that applies to your product depends on its HSN code:

• 0% (Exempt): Essential food items — fresh produce, grains, milk, eggs, meat in natural form
• 5%: Packaged food, edible oils, spices, sugar, fertilisers, economy hotels, transport
• 12%: Processed foods, computers, mobile phones, business class travel
• 18%: Most manufactured goods, financial services, restaurants, IT services, capital goods
• 28%: Luxury goods, automobiles, tobacco, aerated drinks, cement

For the full standard GST invoice format with CGST/SGST fields, download the GST Invoice Format template.

How Ledgerly Automates All GST Calculations

Instead of manually calculating CGST, SGST or IGST on every invoice, Ledgerly's GST Billing App does all the calculation automatically. You assign a GST rate to each product once. When you create an invoice, the app:

• Calculates the GST amount for each line item based on the assigned rate
• Splits the total GST into CGST and SGST (intrastate) or shows IGST (interstate) based on the customer's state
• Sums all line items to give the correct total invoice value
• Prints all values — taxable amount, CGST, SGST and total — clearly on the invoice

No manual calculation. No risk of arithmetic errors. No wrong GST rate on the wrong product. Every invoice is correct automatically.

Frequently Asked Questions

If a product has 12% GST, how much is CGST and SGST each?

For intrastate supplies at 12% GST: CGST = 6% and SGST = 6%. The total GST rate is always split equally between CGST and SGST for intrastate transactions. For interstate, it would be IGST at the full 12%.

How do I calculate GST on an invoice with multiple items at different rates?

Calculate the GST for each line item separately based on its own rate, then sum all the GST amounts. For example, one item at 5% and another at 18% — calculate each individually and add the CGST and SGST totals at the bottom. Ledgerly does this automatically for every invoice.

Is GST calculated on the discounted price or the original price?

GST is calculated on the discounted price (after discount), not the original MRP. If you give a 10% discount on a ₹1,000 product, the taxable value is ₹900 and GST is charged on ₹900.

Where can I quickly calculate GST for any amount?

Use the free Ledgerly GST Calculator — enter the amount, select the GST rate and choose GST-inclusive or exclusive. It instantly shows the base amount, CGST, SGST and total.