GST invoice format for services: every field the law asks for

The short answer. A GST tax invoice for services must show your name, address and GSTIN, a unique invoice number of up to 16 characters, the date, the client's details, the SAC code, a description, the taxable value, and the rate and amount of each tax. Inter-state invoices also need the place of supply. Issue it within 30 days of finishing the work.

Which document to issue

Not every bill is a tax invoice. Pick the one that matches your situation:

If you are not registered, you cannot charge GST or call your bill a tax invoice. The GST guide for freelancers explains when registration starts.

Every field on a tax invoice for services

Rule 46 of the CGST Rules lists what a tax invoice must contain. For services, that means:

If you sell to an unregistered client for less than ₹50,000, you only need their address details if they ask for them. Businesses above the e-invoicing limit also need a QR code with the invoice reference number (IRN); more on that below.

Invoice numbering rules

The invoice number must:

• be 16 characters or fewer,
• use only letters, numbers, hyphens (-) and slashes (/),
• run consecutively, and
• be unique within a financial year.

You can keep more than one series, for example one per business line, and you can restart numbering each April as long as no number repeats within a year. Putting the financial year in the number keeps it unique: INV/26-27/001 is 13 characters. Every invoice number you issue is reported in your GSTR-1 return, so gaps and duplicates are visible.

When to issue the invoice

For services, issue the tax invoice within 30 days of the date the service is supplied. You can issue it earlier, including before the work starts.

For ongoing work such as retainers, the rules are tied to payment:

• If the contract fixes a due date for payment, invoice on or before that date.
• If it does not, invoice when you receive payment.
• If payment is linked to milestones, invoice on or before the date each milestone is completed.

When a client pays an advance, issue a receipt voucher for it, and a refund voucher if the work then does not go ahead.

Copies

Make the tax invoice in two copies: "Original for recipient" for the client and "Duplicate for supplier" for your records. An invoice sent as a PDF counts as an electronic invoice, so it does not need a handwritten signature.

A sample invoice

A design studio registered in Maharashtra bills a client in Mumbai, also registered in Maharashtra:

Above the table: the studio's name, address and GSTIN, the invoice number (for example INV/26-27/014), the date, and the client's name, address and GSTIN. Below it: "Tax payable on reverse charge: No".

If the same studio billed a client registered in Karnataka, the two tax lines would become one, IGST at 18%: ₹14,400, and the invoice would add "Place of supply: Karnataka".

E-invoicing: only above ₹5 crore

E-invoicing means registering each B2B invoice on the government's Invoice Registration Portal to get an IRN and a QR code. It is compulsory only for businesses whose aggregate turnover has exceeded ₹5 crore in any financial year since 2017-18. There was no change to this limit in 2025 or 2026. Most freelancers and small agencies are well below it.

Common mistakes

• Charging GST before you are registered. Only a registered person can collect it.
• The wrong tax type. CGST + SGST on an inter-state invoice, or IGST within the state, means the tax was paid to the wrong government and has to be corrected.
• No place of supply on an inter-state invoice.
• Invoice numbers that repeat or run out of order, often from keeping invoices in several spreadsheets.
• Issuing the invoice months late. The 30 day limit applies even if the client has not paid.
• Adding GST to the margin. GST you collect is not income; work out your profit on the amount before tax. See margin vs markup.

Where sync.d fits

sync.d numbers invoices in one sequence per account, picks IGST or CGST + SGST from your GSTIN state and the client's place of supply, and lets you set a default SAC code for new lines. It has eleven invoice templates and PDF download, and the monthly CSV export puts IGST, CGST and SGST in separate columns for your CA. If you only need a one off invoice, the free invoice generator makes a PDF without signing up.