If you invoice from India, your PDF isn’t just a “please pay me” note — it’s a tax document. Get the GST split wrong and two things happen: your client’s accountant sends it back, and you look like you don’t know what you’re doing. Neither helps you get paid.
The 10-second rule
Same state as your client? Charge CGST + SGST — each is half the total GST rate.
Different state? Charge IGST — the full GST rate as a single line.
Example at 18% GST on ₹50,000:
- Intra-state (e.g. you in Karnataka, client in Karnataka): CGST 9% (₹4,500) + SGST 9% (₹4,500) = ₹9,000 tax
- Inter-state (e.g. you in Karnataka, client in Maharashtra): IGST 18% (₹9,000) = ₹9,000 tax
Same total tax. Different line items. That’s the whole game.
How do you know the state?
Two ways:
- GSTIN first two digits — they’re the state code. 29 = Karnataka, 27 = Maharashtra, 07 = Delhi, etc.
- Place of supply — for most B2B services, it’s where the client is registered. When in doubt, ask for their GSTIN before you invoice.
BillFast reads the GSTIN prefix (or the state you pick) and applies CGST+SGST or IGST automatically. One less thing to Google at midnight.
What about HSN and SAC?
Goods use HSN codes. Services use SAC codes. Most freelance work is services — design, dev, consulting, content.
Common SAC examples:
- 998314 — IT design and development
- 998313 — IT infrastructure and network management
- 998391 — Other professional, technical, and business services
Put SAC on every line item. Your client needs it for their Input Tax Credit (ITC). Missing SAC = invoice bounces back = you wait longer for money.
Mistakes that actually happen
- Charging IGST to a client in your own state — their CA will reject it.
- Splitting CGST/SGST for an out-of-state client — same problem, opposite direction.
- No GSTIN on a B2B invoice — if they’re registered, you need their GSTIN. Full stop.
- Wrong invoice number sequence — must be consecutive per FY. Don’t reuse or skip randomly.
Getting paid is still the real product
A perfectly compliant GST invoice sitting in someone’s inbox unpaid is still ₹0 in your account. Put your UPI ID and a Razorpay payment link on the PDF itself — not in a separate email three days later.