What a GST invoice must contain, when it is CGST and SGST versus IGST, and the invoice numbering rule that trips people up at filing time.
Step by step
Check the client state The place of supply decides the tax heads. Same state as you means CGST plus SGST; a different state means IGST at the full rate.
Add the line items Describe the service, add the SAC code if you use one, and set the rate. Most professional services are 18%.
Let the split compute Retainer applies the correct heads from the client's state rather than asking you to pick, which is where manual invoices go wrong.
Send it The invoice goes out as a link and a PDF, with a UPI link on it so the client can pay immediately.
A GST invoice is a document with legal requirements, not a formatted receipt. If your client is claiming input tax credit on it, and a business client will be, the details have to be right or their credit is at risk, which quickly becomes your problem.
What a tax invoice must contain
your name, address and GSTIN
a consecutive invoice number, unique within the financial year
the date of issue
your client's name, address and GSTIN if they are registered
the place of supply, and the state code
a description of the service, with the SAC code
the taxable value, the rate, and the tax amount split into CGST and SGST or shown as IGST
whether the tax is payable on reverse charge
your signature or digital signature
CGST and SGST, or IGST
One rule, and it follows your client's location, not yours. A client in your own state pays CGST and SGST at half the rate each. A client in another state pays IGST at the full rate. The total tax is identical either way, and an export of services is a separate case again, zero-rated where the conditions are met.
Where your client is
On an 18% invoice
Same state as you
CGST 9% + SGST 9%
Another state
IGST 18%
Outside India
Zero-rated, conditions apply
The numbering rule people get wrong
Invoice numbers must be consecutive and unique within a financial year, and may not exceed sixteen characters. Restarting the series mid-year, reusing a number after deleting an invoice, or running two parallel series in one spreadsheet are all real problems at filing time. Retainer refuses a number that would repeat inside a financial year rather than letting you discover it in October.
If you are not registered
Below the registration threshold you do not charge GST, and you issue a bill of supply rather than a tax invoice. Leave your GSTIN blank and Retainer bills without tax. Registration becomes mandatory above ₹20 lakh of annual turnover, and ₹10 lakh in some special category states.
Rates and rules change. Confirm your SAC code and rate against the primary source, the Central Board of Indirect Taxes and Customs (cbic.gov.in), or ask your CA.
Frequently asked
When do I charge CGST and SGST instead of IGST?
When the place of supply is your own state. A client in another state is charged IGST at the full rate instead. The total tax is the same; only the heads differ, and they follow your client's location rather than yours.
What GST rate applies to freelance services?
Most professional services, including design, development, writing and consulting, are taxed at 18%. Confirm the SAC code for your specific service against CBIC guidance.
Can my invoice numbers restart every year?
Yes, and they usually should. The requirement is that the series is consecutive and unique within a financial year, and no more than sixteen characters.
Do I charge GST to a client outside India?
An export of services is zero-rated where the conditions are met, which includes being paid in convertible foreign exchange. The rules are specific, so confirm your case with your CA.
What if I am not GST-registered?
You do not charge GST and you issue a bill of supply instead of a tax invoice. Registration is mandatory above ₹20 lakh of annual turnover, and ₹10 lakh in some states.