GST invoice format: every field a tax invoice needs
If you are registered under GST, the invoices you issue for taxable supplies must be tax invoices with specific details. Your client needs those details to claim input tax credit, so a missing GSTIN or a wrong place of supply can delay your payment. This guide lists every field, with an example for a service business.
Mandatory fields on a GST tax invoice
CGST Rule 46 lists what a tax invoice must contain. For a service business billing another business, that means:
| Field | Example |
|---|---|
| Your name, address and GSTIN | Iyer & Co, Bengaluru · 29AAACI1195H1ZI |
| Invoice number, unique for the financial year | INV/26-27/41 |
| Date of issue | 1 November 2026 |
| Client's name, address and GSTIN (if registered) | Sharma Traders · 29AAGCS4581C1Z8 |
| SAC code for services (HSN for goods) | 998222 (accounting and bookkeeping) |
| Description of the service | Monthly bookkeeping, October 2026 |
| Quantity and unit, where applicable | 1 month, or hours |
| Taxable value, after any discount | ₹15,000.00 |
| Tax rate and amount, split by CGST, SGST/UTGST or IGST | CGST 9% ₹1,350 · SGST 9% ₹1,350 |
| Place of supply (state name and code) | Karnataka (29) |
| Whether tax is payable on reverse charge | No |
| Signature or digital signature of the supplier | For Iyer & Co, Authorised Signatory |
Billing an unregistered client above ₹50,000? Also include their name, address and state.
Invoice numbering rules
- At most 16 characters.
- Only letters, digits, hyphen (-) and slash (/).
- Unique within the financial year (April to March). Most businesses restart at 1 every April and put the year in the number, like INV/26-27/1.
- Consecutive: don't skip numbers or reuse a cancelled one.
CGST and SGST, or IGST?
It depends on the place of supply. For services to a registered business, that is normally the client's registered location, which is the state code in the first two digits of their GSTIN.
- Same state as you (intra-state): charge CGST and SGST, each at half the rate. 18% becomes 9% + 9%.
- Different state (inter-state): charge IGST at the full rate.
Use the GST calculator to split any amount, and the GSTIN validator to check the client's GSTIN and state before you invoice.
SAC codes for services
Services use SAC codes (Services Accounting Codes). If your aggregate turnover is up to ₹5 crore, at least 4 digits are required on B2B invoices; above ₹5 crore, 6 digits. Using the full 6-digit code is the safe default. Some common ones for service businesses:
| SAC | Service |
|---|---|
| 998221 | Financial auditing services |
| 998222 | Accounting and bookkeeping services |
| 998231 | Corporate tax consulting and preparation |
| 998311 | Management consulting and management services |
| 998314 | IT design and development services |
| 998361 | Advertising services |
| 998391 | Specialty design services (interior, industrial, graphic) |
Check the exact code for your service against the official SAC list or with your CA.
When to issue the invoice
For services, issue the tax invoice within 30 days of supplying the service (45 days for banks and some financial institutions). For monthly retainers, invoicing at the start or end of each month keeps you well inside the limit.
What if you are not GST-registered?
You cannot charge GST. Issue a plain invoice without GSTIN or tax lines. Service businesses usually need to register once turnover crosses ₹20 lakh (₹10 lakh in some special-category states), or earlier for inter-state supplies in some cases.
E-invoicing
If your aggregate turnover has exceeded ₹5 crore in any financial year since 2017-18, B2B invoices must also be registered on the Invoice Registration Portal to get an IRN and QR code. Above ₹10 crore, invoices must be reported within 30 days of issue. Below the threshold, a correctly formatted tax invoice is enough.
Common questions
Can an invoice number contain the financial year?
Yes. INV/26-27/1 is 12 characters and uses only allowed characters. Keep the whole number within 16 characters.
Is a signature required on a GST invoice sent by email?
Rule 46 requires a signature or digital signature of the supplier. Many small businesses use an "Authorised Signatory" block on emailed invoices; for e-invoices, the IRN signature applies. Ask your CA what suits your clients.
What GST rate applies to bookkeeping and consulting?
Most professional services, including accounting, bookkeeping and management consulting, are taxed at 18%.
This guide explains common practice and is not tax or legal advice. Rules change; confirm anything that affects your filings with your CA.
EasyInvoices fills in every one of these fields for you and picks CGST + SGST or IGST from your client's GSTIN.
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