How to Create a GST Invoice: Complete Guide for Indian Businesses (2026)

1GST Invoice Mandatory Fields

Under Rule 46 of the CGST Rules 2017, every tax invoice issued by a registered person must contain specific information. Missing any of these fields can make your invoice non-compliant, which means your buyer cannot claim input tax credit on the purchase. The government designed these requirements to create a transparent audit trail for every taxable transaction. Understanding each field is essential whether you create invoices manually or use a GST invoice generator tool. Let us examine every mandatory field that your GST invoice must include to satisfy both legal requirements and practical business needs.

2Understanding GSTIN Format

The GSTIN (GST Identification Number) is a 15-digit alphanumeric code assigned to every registered taxpayer in India. Understanding its structure helps you validate GSTINs on invoices you receive and ensures you enter your own correctly. The first two digits represent the state code as per Indian census data. Digits three through twelve correspond to the PAN (Permanent Account Number) of the entity. The thirteenth digit indicates the number of registrations within a state under the same PAN. The fourteenth digit is always the letter Z by default, serving as a placeholder for future use. The fifteenth digit is a checksum character calculated using an algorithm to detect data entry errors.

For example, a GSTIN like 27AABCU9603R1ZM tells you that the business is registered in Maharashtra (state code 27), has PAN AABCU9603R, this is their first registration in the state (digit 1), followed by the default Z and the checksum M. When using our GST invoice generator, the tool automatically validates GSTIN format to catch typos before you generate your invoice. Always verify recipient GSTINs against the official GST portal at services.gst.gov.in to ensure accuracy. Incorrect GSTINs on invoices will be flagged during GST return filing and can delay input tax credit claims for your buyer.

3HSN and SAC Codes Explained

HSN (Harmonized System of Nomenclature) codes classify goods, while SAC (Services Accounting Codes) classify services under the GST regime. These codes determine the applicable tax rate for each item on your invoice and are mandatory for GST compliance. For businesses with annual turnover up to Rs. 5 crore, a 4-digit HSN code is required on invoices. Businesses with turnover exceeding Rs. 5 crore must use 6-digit HSN codes. The number of digits you need depends on your turnover bracket, so check your annual aggregate turnover to determine the correct requirement for your business.

Finding the correct HSN or SAC code is critical because using the wrong code means applying the wrong tax rate, which leads to compliance issues during return filing. Common examples include HSN 6109 for t-shirts (taxed at 5% for value up to Rs. 1000), HSN 8471 for computers (taxed at 18%), and SAC 9983 for professional and management consulting services (taxed at 18%). The government publishes the complete HSN and SAC code directories on the CBIC website. Our GST invoice generator includes a searchable database of commonly used codes so you can quickly find and apply the correct classification without switching to external reference materials while creating your invoices.

4CGST vs SGST vs IGST: Place of Supply Rules

The type of GST you charge depends entirely on the place of supply relative to your business location. For intra-state transactions where both the supplier and recipient are in the same state, you charge CGST (Central GST) and SGST (State GST) in equal parts. For example, if a Delhi-based consultant bills a Delhi-based client at 18% GST, the invoice shows 9% CGST (Rs. 900) and 9% SGST (Rs. 900) on a taxable value of Rs. 10,000. The central government collects CGST while the state government collects SGST. This dual structure is the foundation of India's GST architecture and replaces the previous system of separate central and state indirect taxes.

For inter-state transactions where the supplier and recipient are in different states, you charge IGST (Integrated GST) at the full rate. Using the same example, a Delhi-based consultant billing a Mumbai-based client at 18% GST would show IGST of Rs. 1,800 on the invoice instead of splitting it into CGST and SGST. The central government collects IGST and later settles the state's share. The place of supply rules under Sections 10 to 13 of the IGST Act determine which state receives the tax revenue. Our GST invoice generator automatically applies the correct tax type based on the supplier and recipient state codes you enter, eliminating manual calculation errors that are common in inter-state billing.

5E-Invoicing Requirements in 2026

E-invoicing is the government's system for real-time validation and registration of B2B invoices through the Invoice Registration Portal (IRP). When e-invoicing applies to your business, you must generate a unique Invoice Reference Number (IRN) and QR code for every B2B invoice before sharing it with your buyer. The IRP validates your invoice data against the GST system and returns a signed JSON with the IRN and a digitally signed QR code. This process happens through API integration or the government portal. As of 2026, e-invoicing is mandatory for all businesses with aggregate annual turnover exceeding Rs. 5 crore across all financial years since GST implementation.

The threshold has been progressively lowered over the years from Rs. 500 crore when e-invoicing launched in October 2020, to Rs. 100 crore in 2022, Rs. 10 crore in 2023, and Rs. 5 crore currently. Industry expectations suggest the government will eventually mandate e-invoicing for all GST-registered businesses regardless of turnover. Even if your business falls below the current threshold, preparing for e-invoicing now is a wise decision. Our GST invoice generator produces invoices with all fields required by the e-invoicing schema, so your data is already structured correctly when you need to register invoices on the IRP. This forward-compatible approach means transitioning to mandatory e-invoicing will require minimal changes to your workflow.

6Common GST Invoice Mistakes to Avoid

Even experienced business owners make GST invoice errors that lead to compliance notices and delayed input tax credit claims. The most frequent mistake is entering an incorrect or unverified GSTIN for the recipient. Since buyer GSTIN directly affects their ability to claim input tax credit, a single wrong digit can cause significant problems during return reconciliation. Always verify GSTINs on the official portal before issuing invoices. The second common error is using wrong HSN or SAC codes, which results in incorrect tax rates being applied. This triggers mismatches during GSTR-2A and GSTR-2B reconciliation for your buyers and can invite scrutiny from tax authorities.

Another frequently overlooked mistake is applying the wrong tax type for inter-state versus intra-state transactions. Charging CGST plus SGST on an inter-state sale, or IGST on an intra-state sale, is a compliance violation regardless of whether the total tax amount is correct. The place of supply must always determine the tax type. Additional errors include non-sequential invoice numbering, missing place of supply on the invoice, not showing tax breakup separately for each line item, and issuing invoices after the prescribed time limit. For goods, invoices must be issued before or at the time of delivery. For services, invoices must be issued within 30 days of providing the service. Using a dedicated GST invoice tool that enforces these rules automatically eliminates the majority of these common errors.

7Step-by-Step: Create a GST Invoice with Our Tool

Creating a compliant GST invoice using OnlineInvoiceMaker.com's GST invoice generator takes just a few minutes. Follow these steps to produce an invoice that meets every GST requirement.

8Frequently Asked Questions

Conclusion: Stay GST Compliant Without the Complexity

Creating GST-compliant invoices does not have to be complicated or expensive. With a clear understanding of mandatory fields, GSTIN structure, HSN/SAC codes, and the CGST versus SGST versus IGST rules, you can confidently issue invoices that satisfy every legal requirement. Our free GST invoice generator automates the technical details like tax type selection and calculation so you can focus on running your business. Whether you are a small shop owner in Jaipur or a software consultant in Bangalore, compliant invoicing is now just a few clicks away.