GST Invoice Rules: Mandatory Fields, Copies & Time Limits
A tax invoice is the backbone document of GST — it decides your output liability and your customer's input tax credit. This guide walks through what a valid invoice must contain, when it must be issued, and the related documents every business should know.
The mandatory fields (Rule 46 checklist)
The CGST Rules prescribe the contents of a tax invoice. In practical checklist form, a valid tax invoice should carry:
- Supplier details — your name, address and GSTIN.
- Invoice number — a consecutive serial number (up to 16 characters, letters/numerals and permitted symbols), unique for the financial year.
- Date of issue.
- Recipient details — name, address and GSTIN if the buyer is registered. For unregistered buyers, above the prescribed value, the name, address and place of supply must still be recorded.
- HSN or SAC code for each item — the number of digits required depends on your turnover.
- Description, quantity and unit of the goods, or description of the services.
- Taxable value of each supply, after any discount shown on the invoice.
- Tax rate and tax amount — CGST + SGST for intra-state supplies, IGST for inter-state, shown separately.
- Place of supply with the state name, essential for inter-state invoices.
- Reverse charge indication, where tax is payable by the recipient.
- Signature or digital signature of the supplier or an authorised representative (not required on a valid e-invoice with QR code).
Our free GST Invoice Generator lays these fields out for you — seller and buyer blocks, HSN column, per-item GST, automatic CGST/SGST vs IGST based on the place of supply, and amount in words.
Intra-state vs inter-state: which taxes appear
If your state and the place of supply are the same, the invoice shows the GST split equally into CGST and SGST. If they differ, a single IGST line appears at the full rate. Getting this wrong is one of the most common invoice defects — the total tax is identical, but paying the wrong head creates refund-and-repay headaches. Our CGST vs SGST vs IGST guide explains the logic, and both our invoice tool and GST calculator handle the split automatically.
How many copies?
For goods, prepare the invoice in triplicate: the original for the recipient, a duplicate for the transporter and a triplicate for your own records. For services, duplicate is enough — original for the recipient, duplicate for the supplier. With e-invoicing and digital records this is less visible day-to-day, but the rule still shapes how printed invoices are marked ("Original for Recipient", and so on).
When must the invoice be issued?
For goods, the invoice must be issued at or before the removal or delivery of the goods. For services, you have up to 30 days from the date the service is supplied (45 days for banks and certain financial institutions). Raising invoices late doesn't just risk penalties — it pushes tax into the wrong return period and delays your customer's input credit, which strains the relationship.
Tax invoice vs bill of supply
Not every sale gets a tax invoice. If you are a composition dealer, or the supply is exempt, you issue a bill of supply instead — it looks similar but must not show any tax amount, and a composition dealer must state on it that composition tax is not collectible from the buyer. Issuing a "tax invoice" with GST when you're on composition is a serious violation.
Small-value relaxation
For sales below ₹200 to unregistered buyers who don't ask for an invoice, you may skip individual invoices and issue one consolidated invoice at the end of the day covering all such sales. Retail counters rely on this daily.
E-invoicing in brief
Businesses above the notified aggregate turnover threshold must register B2B invoices on the government's Invoice Registration Portal (IRP), which returns an IRN and a signed QR code that must appear on the invoice. The threshold has been lowered in stages over the years, so if your turnover is in crores, check the current limit on the GST portal or with your CA before assuming you're outside the system. E-invoicing does not change what an invoice contains — the Rule 46 fields above still apply — it changes how the invoice is reported.
Credit and debit notes: fixing an issued invoice
You never edit or reissue a tax invoice after the fact. If the taxable value or tax charged turns out too high (price revision, returns, deficiency), issue a credit note; if too low, a debit note. Both reference the original invoice and flow through your returns, keeping the audit trail intact.
Practical tips that prevent notices
Lock your serial series on day one of the financial year and never reuse or skip numbers casually — gaps invite questions. Verify your customer's GSTIN before invoicing a new B2B buyer; a mistyped GSTIN means their credit doesn't flow and you'll be re-doing paperwork — our GSTIN Validator catches format and checksum errors instantly. Show discounts on the invoice, since only invoice-linked discounts reduce the taxable value cleanly. And keep quotations, proformas and invoices clearly separated — see Quotation vs Invoice vs Proforma for why mixing them causes trouble.