Good GST billing software applies the right HSN/SAC code and CGST/SGST or IGST split on every invoice automatically, generates a valid e-Invoice IRN once your turnover crosses ₹5 crore, keeps billing when the internet drops, and includes these GST fields on its free tier — not just a generic tax box.
"GST billing software" covers a huge range of tools, from a generic invoice template with a tax field bolted on to software that genuinely automates HSN/SAC codes, tax splits, and e-Invoice IRNs. This guide covers what actually separates the two, with a checklist you can run against any app before you commit to it.
Does it apply HSN/SAC codes automatically?
Every GST invoice line needs an HSN (goods) or SAC (services) code, and the required number of digits depends on your turnover: at least 4 digits on B2B invoices if your aggregate annual turnover is up to ₹5 crore, and at least 6 digits above that. The useful version of this feature stores the code once per item and applies it to every future invoice — not a free-text field you retype each time you bill. See our HSN/SAC codes guide for how the digit rules work.
Does it split CGST/SGST vs IGST correctly?
If the buyer is in the same state as your registered business, GST splits into CGST and SGST at half the rate each; a buyer in a different state means IGST at the full rate. The split has to be decided per invoice from the place of supply — a flat "GST rate" field that doesn't do this is a compliance gap that surfaces at reconciliation time.
| Sale | Taxable value | GST rate | What the invoice shows |
|---|---|---|---|
| Seller in Gujarat, buyer in Gujarat | ₹10,000 | 18% | CGST 9% = ₹900 + SGST 9% = ₹900 |
| Seller in Gujarat, buyer in Maharashtra | ₹10,000 | 18% | IGST 18% = ₹1,800 |
Does it generate a valid e-Invoice IRN, if you need one?
e-Invoicing is mandatory for B2B invoices once your aggregate annual turnover has exceeded ₹5 crore in any financial year from 2017-18 onward. Those invoices must be reported to the Invoice Registration Portal (IRP), which returns an IRN and a signed QR code that must appear on the invoice. If your turnover is ₹10 crore or more, invoices must also be reported within 30 days of the invoice date. "e-Invoice ready" in a product description isn't the same as integrating with the IRP — check whether the software produces a real IRN, or just a field you fill in from somewhere else.
Is it up to date with the 2025 GST rate changes?
From 22 September 2025, most goods moved to two main GST slabs — 5% and 18% — with a 40% rate for specified demerit goods, and the 12% and 28% slabs largely removed. Billing software that still defaults items to old rates will produce invoices that don't match your returns. Check that rates are set per item and easy to update when the GST Council changes them.
Does the free tier actually include GST fields?
A lot of "free GST billing software" turns out to be a free invoice template with the GST-specific fields — HSN/SAC, tax splits, e-Invoice support — gated behind a paid plan. Before assuming a free tier covers you, check specifically whether it handles GST invoicing, not just invoicing in general, and whether it caps the number of invoices per month.
Does it hold up with a patchy connection?
Plenty of billing software is cloud-only, which becomes a real problem the moment a shop counter's signal drops mid-sale. Offline-first software keeps billing working with no connection and syncs once you're back online — worth testing directly by switching your phone to airplane mode during a trial, rather than assuming a mobile app implies offline support.
A short checklist
Run every candidate app through these eight checks before you move your billing onto it:
- HSN/SAC stored per item — set once, applied to every invoice, with the right digit length for your turnover.
- Automatic CGST/SGST vs IGST — decided from the buyer's state on each invoice, not a single default.
- Current GST rates — the 5% / 18% / 40% structure from 22 September 2025, editable per item.
- Real e-Invoice IRN — generated through the IRP with a QR code, if your turnover is above ₹5 crore (or will be soon).
- All required invoice fields — GSTIN, serial number, place of supply, reverse-charge flag, and buyer GSTIN for B2B.
- Works offline — test billing in airplane mode, then confirm it syncs cleanly afterwards.
- Free tier includes GST — no paywall on HSN/SAC or tax splits, and no low monthly invoice cap.
- Clean exports for your accountant — sales and purchase registers in Excel or CSV, ready for GSTR filing.
StashBill's GST/VAT compliance engine covers HSN/SAC automation, CGST/SGST/IGST splits, and offline billing — see the full India GST invoice requirements, and pricing for what's included free.
Frequently asked
Is free GST billing software actually usable for real invoicing?
It can be — but check specifically whether HSN/SAC codes and CGST/SGST/IGST splits are included in the free tier, and whether there's a monthly invoice cap, rather than assuming a free plan covers GST invoicing.
Do small businesses need e-Invoicing?
Only if aggregate annual turnover has exceeded ₹5 crore in any financial year since 2017-18. Below that, an IRN isn't required on your invoices, though HSN/SAC codes still are on B2B invoices.
What's the difference between GST billing software and a general invoicing app?
GST billing software automates HSN/SAC codes, the CGST/SGST/IGST split, and e-Invoice IRN generation; a general invoicing app may only offer a flat tax-rate field that doesn't match what GST filing actually requires.
Sources
- CBIC — CGST Act, Rules (Rule 46: tax invoice) and notifications
- GST e-Invoice System (Invoice Registration Portal)
- GST Portal — rate notifications and advisories
General information, not tax advice. Thresholds and rates are current as of October 2026 — confirm with the GST portal or your accountant before relying on them.