Billing basics: what every invoice must include

Billing Basics By Bahify Team ·

Half of the GST-filing headaches we see come from invoices that are almost right. They have the customer, the amount, sometimes even the tax — but they’re missing one or two of the fields that actually matter. Here’s the short list.

What every GST invoice must include

  • Your business name, address and GSTIN.
  • A unique, sequential invoice number — no gaps, no repeats, per financial year.
  • Date of issue.
  • Buyer name, address, and GSTIN (GSTIN is mandatory if the buyer is registered).
  • HSN or SAC code for each item or service.
  • Description, quantity and unit for each line.
  • Taxable value, tax rate, and tax amounts — split as CGST + SGST (intra-state) or IGST (inter-state).
  • Total invoice value, in both numbers and words.
  • Place of supply, especially for inter-state transactions.
  • Signature (digital or physical) of the supplier.

HSN vs SAC — quick refresher

HSN (Harmonised System of Nomenclature) is for goods. SAC (Services Accounting Code) is for services. The granularity required depends on your turnover; Bahify defaults to the right depth for your tier.

When e-invoicing applies

If your turnover crosses ₹5 crore in any financial year from 2017-18 onwards, you have to generate e-invoices — meaning the invoice is registered on the IRP portal and gets an IRN (Invoice Reference Number) before you can issue it. Below ₹5 crore: not required.

Fixing mistakes — credit and debit notes

If you over-billed, returned goods, or gave a discount after the fact, you don’t edit the original invoice. Issue a credit note with a clear reference to the original. Conversely, if you under-billed, issue a debit note. Both flow into GSTR-1 just like invoices.

Three habits that keep audits painless

  1. Never skip an invoice number. Gaps trigger questions during audits.
  2. Reconcile every month, not every year. Tiny mistakes are easy to fix when fresh; impossible to remember six months later.
  3. Keep PDFs of every invoice you send. Cloud storage, not someone’s laptop.

Bahify generates GST-compliant invoices out of the box — the required fields are all in place, sequential numbering is automatic, and credit / debit notes are first-class objects.

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