Invoice Number Generator

What is an invoice number?

An invoice number is a unique serial identifier printed on every invoice you issue. It lets you and your customer refer to a specific transaction, keeps your accounts in order, and links each sale to your GST returns. A good invoice number is not random. It is part of a continuous, consecutive series so that no two invoices share a number and there are no gaps. The tool above builds that series for you from a prefix, the financial year and a padded running number, and previews the next five numbers you can copy straight into your invoice.

GST rules for invoice numbers

Under Rule 46(b) of the CGST Rules, the invoice serial number must follow four conditions. Getting these right keeps your invoices valid and your GSTR filings clean.

A good invoice number format

The most common and audit-friendly format combines a prefix, the financial year, and a zero-padded sequence, for example INV/2026-27/0001. The prefix identifies the document type or branch, the year resets your series cleanly each April, and the padding keeps numbers the same width so they sort correctly. Here are a few valid patterns:

Should the numbering reset each year?

Yes. It is standard practice to start a fresh series at the beginning of each financial year (1 April in India), usually by including the year in the number. This keeps each year self-contained and easy to reconcile, while still meeting the unique and consecutive requirements within that year. Maintain separate series for different document types, so tax invoices, credit notes, debit notes and delivery challans each have their own running numbers rather than sharing one.

Common invoice numbering mistakes

• Leaving gaps in the series, which raises questions in an audit.
• Duplicating a number, often after switching software mid-year.
• Exceeding 16 characters or using spaces and special characters that GST does not allow.
• Mixing invoices and credit notes in the same series instead of separate ones.

Why consistent invoice numbers matter

A clean, unbroken numbering series is more than tidiness. It is what lets your buyer claim input tax credit against the exact invoice, what your accountant uses to reconcile sales with your GSTR-1, and what an auditor looks at first to check nothing is missing or duplicated. Gaps or repeats suggest invoices were cancelled without record or issued outside the books, which invites scrutiny. A predictable format also makes day-to-day work faster: you can tell at a glance which financial year and branch an invoice belongs to, and searching your records becomes trivial. Setting the pattern once, at the start of the year, saves you from fixing a tangled series later.

Then create the invoice

Once you have your number, create a GST invoice or a quotation and paste it in. Work out the tax on the total with the GST calculator, and spell the amount with the rupees in words converter. New to invoicing? Read the GST invoice format guide and the difference between a bill, invoice and receipt.

Frequently asked questions