What a GST tax invoice legally needs
A GST-compliant tax invoice isn't just a bill with a total — it needs a specific set of fields to be legally valid: your GSTIN, a unique invoice number and date, the customer's name and GSTIN (for B2B), a description of goods or services with HSN/SAC codes, taxable value, applicable GST rate, and the CGST/SGST or IGST amount split out separately.
Missing any of these — especially the HSN code or the tax split — is one of the most common reasons an invoice gets flagged during a GST audit.
The mistakes that trip up small businesses
The two most frequent errors are charging CGST+SGST on an inter-state sale (it should be IGST), and skipping the HSN summary entirely for B2C sales below the reporting threshold — where it is still good practice to include it.
A close third is invoice numbering that resets inconsistently across a financial year, which makes GSTR-1 reconciliation painful later.
LedgrBook handles this automatically. The parts of this guide your bills already know.
See how →Self-audit checklist
Before you send an invoice, check: GSTIN present and correctly formatted, invoice number sequential within the financial year, correct tax type (CGST/SGST vs IGST) based on the customer's state, HSN code on every line item, and totals that match the tax calculation exactly to the rupee.
Software that calculates GST automatically from the HSN code and customer state — like LedgrBook — removes most of this checklist as a manual step.
General information, not professional tax advice — confirm specifics with your CA.
