How to Create a GST Invoice — Complete Guide 2026

If you run a business in India — whether you are a freelancer, a small shop owner, or a growing startup — issuing a proper GST invoice is not optional. It is a legal requirement under the Goods and Services Tax Act, and getting it wrong can lead to penalties, failed audits, and lost input tax credit for your buyers.

This guide walks you through everything: what a GST invoice is, when you need one, every mandatory field required by law, and how to generate one in seconds using our free tool.

What Is a GST Invoice?

A GST invoice is a document issued by a registered supplier to the buyer at the time of sale. It serves as the primary record for both parties to claim or verify input tax credit (ITC). Under the GST regime, this invoice replaces all earlier formats like VAT invoices, service tax invoices, and excise invoices.

Think of it this way: without a valid GST invoice, your buyer cannot claim ITC, and your transaction has no legal tax trail. The GST Council has laid out specific rules under Section 31 of the CGST Act, 2017 that define when and how invoices must be issued.

When Do You Need to Issue a GST Invoice?

You must issue a GST invoice in the following scenarios:

Every time you supply taxable goods or services, you are required to generate a tax invoice before or at the time of delivery (for goods) or within 30 days of supplying the service. If you are running a continuous supply — like a monthly retainer or SaaS subscription — the invoice must be issued before the due date of each payment or before receipt of payment, whichever is earlier.

There are a few exceptions. If you are registered under the composition scheme, you issue a Bill of Supply instead. Similarly, for exempt supplies or when dealing with unregistered buyers for amounts under Rs. 200, a consolidated invoice at the end of the day suffices.

16 Mandatory Fields in a GST Invoice

The Indian government requires every GST invoice to contain specific fields. Missing even one can make the invoice non-compliant. Here is every field you need:

Supplier Details include your business name, full address, and 15-digit GSTIN. This must appear prominently at the top. Your GSTIN format follows a strict pattern: 2 digits for state code, 10 characters from your PAN, 1 digit for entity number, 1 default character "Z", and 1 check digit.

Invoice Number must be unique, sequential, and contain no more than 16 characters. You can use any alphanumeric combination, but it must not repeat within a financial year. A good format is INV-2026-0001.

Invoice Date is the date of issue. For goods, this should be on or before the date of dispatch. For services, within 30 days of completion.

Recipient Details include the buyer's name, address, and GSTIN (if registered). For B2B transactions above Rs. 2,50,000 the buyer GSTIN is mandatory. For B2C transactions, the buyer's name and address are sufficient.

Place of Supply is critical because it determines whether CGST+SGST or IGST applies. This is the state code where the goods are delivered or the service is consumed. Getting this wrong means applying the wrong tax type entirely.

HSN or SAC Code stands for Harmonized System of Nomenclature (for goods) and Services Accounting Code (for services). Businesses with turnover above Rs. 5 crore must mention 6-digit HSN codes. Those between Rs. 1.5 crore and Rs. 5 crore need at least 4-digit codes.

Item Description should clearly identify what was sold. Vague descriptions like "services rendered" can cause issues during audits. Be specific: "Website development — 5 page business site with CMS integration" is far better.

Quantity and Unit must be mentioned for goods. Use standard units like KG, NOS (numbers), MTR (metres), or LTR (litres).

Taxable Value is the total value before tax. This is quantity multiplied by unit price, minus any discounts.

Tax Rate and Amount must be broken down clearly. For intra-state supply (within the same state), show CGST and SGST separately, each at half the total GST rate. For inter-state supply, show IGST at the full rate. For example, if GST is 18 percent, an intra-state invoice shows 9 percent CGST and 9 percent SGST, while an inter-state invoice shows 18 percent IGST.

Total Amount is the final payable amount including all taxes. This must match the sum of taxable value plus all tax components.

Signature or Digital Signature of the supplier or their authorised representative is required. Digital signatures are accepted for electronically generated invoices.

CGST vs SGST vs IGST — Which One to Charge?

This is where most businesses get confused, and it is actually simple once you understand the rule.

If your business is in Maharashtra and your buyer is also in Maharashtra, that is an intra-state transaction. You charge CGST plus SGST, each at half the GST rate. So 18 percent GST becomes 9 percent CGST and 9 percent SGST.

If your business is in Maharashtra but your buyer is in Karnataka, that is an inter-state transaction. You charge IGST at the full rate — 18 percent IGST.

The place of supply determines this, not your location alone. If you are a freelancer in Delhi providing services to a company in Delhi, it is intra-state. If that same company has a branch in Gujarat and the service is consumed there, it becomes inter-state.

HSN and SAC Codes — How to Find Yours

HSN codes classify goods, and SAC codes classify services. Every item on your invoice needs the correct code because it determines the applicable GST rate.

For common services, here are some codes you will encounter frequently: 998314 covers IT consulting and software development, 998313 is for management consulting, 9954 covers construction services, 9964 is for courier and delivery services, and 9971 covers financial and insurance services.

For goods, the codes are more granular. For example, 8471 covers computers and laptops, 6109 covers t-shirts and vests, 0901 covers coffee and tea, and 8517 covers smartphones.

If you are unsure about your HSN or SAC code, our invoice generator has an AI-powered lookup that detects the correct code from your item description automatically.

Common Mistakes That Make Your Invoice Non-Compliant

Over years of helping businesses with invoicing, these are the errors we see most often.

Using the wrong tax type is the most common mistake. Charging IGST on an intra-state supply or CGST/SGST on an inter-state supply invalidates the invoice for ITC purposes. Always verify the place of supply before selecting the tax type.

Missing or incorrect GSTIN happens more often than you would think. A single wrong digit means the invoice cannot be matched during GST return filing. Always validate GSTIN format: it must be exactly 15 characters following the pattern described earlier.

Skipping HSN/SAC codes might not trigger an immediate error, but during audits or return filing, missing codes cause reconciliation failures. As of 2024, even businesses with turnover under Rs. 5 crore are strongly advised to include at least 4-digit codes.

Non-sequential invoice numbers create red flags. If your invoices jump from INV-001 to INV-047, tax authorities may suspect missing transactions. Keep your numbering sequential within each financial year.

Incorrect tax calculations due to rounding errors can compound over hundreds of invoices. Always round tax amounts to two decimal places and ensure the total exactly equals taxable value plus each tax component.

GST Invoice Format for Different Business Types

The core format remains the same, but emphasis shifts depending on your business type.

Freelancers and consultants typically issue service invoices with SAC codes. Your invoices will mostly use codes in the 9983 range. Since most freelancer transactions are B2B, always include the client GSTIN.

E-commerce sellers need to handle both B2B and B2C invoices. For B2C transactions above Rs. 2,50,000 the buyer details become mandatory. You also need to account for TCS (Tax Collected at Source) that the marketplace deducts.

Manufacturers and traders deal with physical goods, so HSN codes, quantities, units of measurement, and delivery details become critical. If the consignment value exceeds Rs. 50,000 you also need an e-Way Bill.

How to Create a GST Invoice in 30 Seconds

Instead of manually formatting invoices in Word or Excel — where you risk missing fields and making calculation errors — use our free GST Invoice Generator.

Here is how it works: enter your business details and GSTIN, add your buyer information, add line items with descriptions, and our AI automatically suggests HSN/SAC codes and the correct GST rate. The tool calculates CGST, SGST, or IGST based on your place of supply selection, generates a professional PDF, and even runs an AI compliance audit to catch errors before you send it.

It takes 30 seconds. 100% free. No watermarks.

Penalties for Non-Compliance

Not issuing a proper GST invoice carries real consequences. Under Section 122 of the CGST Act, failure to issue an invoice can attract a penalty of Rs. 10,000 or the tax amount involved, whichever is higher. For repeated offences, the penalty can escalate to Rs. 25,000.

Beyond penalties, your buyer loses the ability to claim input tax credit, which directly affects their costs. B2B buyers will stop working with suppliers who issue non-compliant invoices because it hurts their bottom line.

Key Takeaways

Every GST invoice needs 16 mandatory fields including GSTIN, HSN/SAC codes, proper tax breakdowns, and sequential numbering. The place of supply determines whether you charge CGST plus SGST or IGST — getting this wrong invalidates the invoice. HSN codes are now practically mandatory for all businesses regardless of turnover. AI tools can eliminate manual errors by auto-detecting HSN codes, calculating taxes, and auditing compliance before you send the invoice.

The easiest way to stay compliant is to stop creating invoices manually. Use a tool that enforces the rules for you.