Whether you're setting up billing software for the first time or you're the accounting guru your team relies on, this guide gives you the complete picture of GST-compliant billing in India — from mandatory invoice fields to advanced automation tips.
GST Invoice Mandatory Fields (Rule 46)
A GST invoice must include all of the following — missing any one can make it legally invalid:
| Field | Required For |
|---|---|
| Supplier's Name, Address & GSTIN | All GST invoices |
| Invoice Number (unique serial) | All GST invoices |
| Date of Issue | All GST invoices |
| Recipient's Name, Address & GSTIN | B2B sales (for an unregistered buyer, name and address when the invoice is ₹50,000 or more) |
| Place of Supply (with State name) | Inter-state supplies (good practice on all) |
| HSN/SAC Code | 4 digits on B2B invoices up to ₹5 crore turnover; 6 digits on all invoices above ₹5 crore |
| Quantity and Unit | Goods |
| Total Value & Taxable Value | All GST invoices |
| CGST + SGST / IGST Amount | All GST invoices |
| Signature (digital or physical) | All GST invoices |
Since 1 August 2023, a business whose turnover has crossed ₹5 crore in any year from 2017-18 must generate e-invoices (IRN + QR code) for its B2B sales. If your turnover is ₹10 crore or more, each e-invoice must also be reported within 30 days of its date. Your billing software should connect to the IRP for this.
Common GST Billing Mistakes to Avoid
- Wrong HSN code — Each product category has a specific HSN code with its own tax rate. Using the wrong HSN can mean under- or over-charging tax. Many items changed rate on 22 September 2025 (GST 2.0), so an old rate left in your item master is now one of the most common errors.
- Mismatched Place of Supply — If the customer is in a different state, you charge IGST (not CGST+SGST). Getting this wrong creates tax liability.
- Missing GSTIN on B2B invoices — Your B2B customer can claim input tax credit only if their GSTIN is on the invoice and you report the invoice against it in GSTR-1.
- Wrong invoice date — Invoice date triggers the tax payment due date. Future-dating invoices is illegal.
- Not reconciling with GSTR-2B — If your purchase invoices don't match your supplier's GSTR-1 filings, your ITC claim will be blocked.
GSTR-1 vs GSTR-3B: What Your Software Should Help With
GSTR-1 reports all your outward sales (invoices issued). Filed monthly or quarterly. Your billing software should auto-populate this from your invoices.
GSTR-3B is your summary return where you declare tax liability and claim ITC. Filed monthly, or quarterly if you are in the QRMP scheme (turnover up to ₹5 crore). Since the July 2025 tax period, the sales-tax figures GSTR-3B picks up from GSTR-1 cannot be edited in GSTR-3B itself, so correct them in GSTR-1A first. Your billing software should give you a ready GSTR-3B summary to verify before filing on the GST portal.
Automating Your Monthly Tax Routine
A good billing software should reduce your monthly GST filing to under 30 minutes:
- All sales auto-captured from POS and invoice module
- GSTR-1 report generated in one click (JSON or Excel format)
- GSTR-3B summary pre-calculated
- ITC from purchases auto-reconciled
- Export to GST portal or send to CA via email
Expert Checklist: Before You Choose Any Billing Software
- ✅ Does it support all GST invoice formats (B2B, B2C, export)?
- ✅ Can it generate GSTR-1 export (JSON format)?
- ✅ Does it handle e-invoicing (IRN generation)?
- ✅ Is data encrypted and automatically backed up?
- ✅ Is there phone/WhatsApp support in Indian business hours?
- ✅ Can you try it free before paying?
Billux covers this list for most shops: B2B and B2C GST invoices, a GSTR-1 JSON export, a GSTR-3B summary, e-invoice IRN generation through the government IRP, nightly backups and WhatsApp support. Start your expert-level billing with a free 7-day trial at billux.in/register.
For the exact field-by-field layout, see our GST invoice format guide, and check your item rates against the new GST rates list after GST 2.0.
Frequently Asked Questions
What is mandatory on a GST invoice?
Under Rule 46: your name, address and GSTIN; a unique invoice number and date; the buyer's details (GSTIN for B2B); HSN or SAC codes; description, quantity and unit; taxable value; tax rate and amount split into CGST and SGST or IGST; place of supply for inter-state sales; and a signature.
How many HSN digits are required on a GST bill?
With turnover up to ₹5 crore, a 4-digit HSN code is mandatory on B2B invoices. Above ₹5 crore, a 6-digit code is required on all invoices. Using the full code also helps your software pick the right GST rate.
Who has to generate e-invoices under GST?
Businesses whose turnover crossed ₹5 crore in any financial year since 2017-18, for B2B sales and exports. Since 1 April 2025, businesses with turnover of ₹10 crore or more must report each e-invoice within 30 days of its date.
Can I edit GSTR-3B figures after filing GSTR-1?
Not the auto-filled sales tax. Since the July 2025 tax period, the liability GSTR-3B picks up from GSTR-1 cannot be edited in GSTR-3B. File GSTR-1A for the same period to correct it before you file GSTR-3B.
What are the most common GST billing mistakes?
Old GST rates left in the item master after GST 2.0, wrong HSN codes, CGST and SGST charged on an inter-state sale that needs IGST, a wrong or missing buyer GSTIN, and filing GSTR-3B without matching it to GSTR-1.
