Getting your invoice format right is the foundation of GST compliance. A correct invoice keeps you audit-ready and protects your customers' input tax credit. A sloppy one creates disputes and lost credit. The good news is that the rules are fixed and simple once you know them.
Mandatory fields on a GST tax invoice
A tax invoice from a GST-registered business must include:
- Your name, address and GSTIN
- A consecutive invoice number (unique for the financial year) and the date
- Customer's name, address, and GSTIN (for B2B)
- HSN code for goods or SAC code for services
- Description, quantity, unit and taxable value of each item
- Tax rate and amount split into CGST + SGST or IGST
- Place of supply (important for inter-state sales)
- Whether tax is charged on a reverse-charge basis
- Signature or digital signature of the supplier
Remember the tax split rule: customer in your state = CGST + SGST; customer in another state = IGST. Our free GST calculator does this for you.
Invoice numbering rules
Your invoice numbers must be consecutive and unique within a financial year. You can use letters, numbers and a few symbols, up to 16 characters. You may run more than one series (for example separate series for retail and wholesale), but each must be continuous with no gaps or duplicates. Random or repeated numbers are a red flag in an audit.
Time limits for issuing an invoice
| Supply type | Issue the invoice… |
|---|---|
| Goods | On or before delivery / removal of goods |
| Services | Within 30 days of providing the service |
How many HSN digits do you need?
The number of HSN digits depends on turnover. As a general rule, smaller businesses (turnover up to ₹5 crore) use 4 digits and larger businesses use 6 digits, with B2B invoices generally needing HSN even for small businesses. Confirm the current requirement, as these rules tighten over time.
Tax invoice vs bill of supply
If you are not registered under GST, or you deal in exempt goods, or you are under the composition scheme, you issue a bill of supply instead of a tax invoice — it looks similar but shows no tax. See our guide on credit and debit notes for how to correct an invoice after it is issued.
Your GST invoice checklist
- ✅ GSTIN, name and address of both parties
- ✅ Unique, consecutive invoice number + date
- ✅ HSN/SAC codes on every line
- ✅ Correct CGST/SGST or IGST split
- ✅ Place of supply for inter-state sales
- ✅ Issued within the time limit
- ✅ Signed (physical or digital)
Doing all of this by hand on every bill is slow and error-prone. This is precisely what billing software is for — pick your item and customer, and every field is filled correctly and automatically.
Create perfect GST invoices in seconds
DAM fills in GSTIN, HSN, tax splits and numbering for you, then prints or shares the invoice — free Gold plan until 31 March 2027.
Download DAM FreeFrequently asked questions
What are the mandatory fields on a GST invoice?
GSTIN and details of both parties, a unique consecutive invoice number and date, HSN/SAC codes, item details, the CGST/SGST or IGST split, place of supply, and the supplier’s signature.
Can I make a GST invoice without software?
Yes, you can create one manually or in a spreadsheet, but you must handle numbering, HSN codes and tax splits yourself. Billing software does this automatically and reduces errors.
Is HSN code compulsory on invoices?
For most GST-registered businesses HSN codes are required, with the number of digits depending on turnover. Smaller businesses typically use 4 digits and larger ones 6.