What is billing, and what is an invoice?
The document that says what was sold, for how much, and what is now owed.
Last checked 20 September 2026
An invoice is the document that records what was sold, to whom, for how much, and what is now owed. Billing is the process of producing it, numbering it, delivering it and collecting against it. Under GST the invoice also does a second job: it is the instrument that passes input tax credit to your buyer.
What an invoice is actually for
Most people think of an invoice as a demand for payment. It is that, but it is doing at least four jobs at once:
| Job | Who it matters to |
|---|---|
| A record of what was supplied and on what terms | Both sides, when there is a dispute |
| A demand for payment, with a due date | You, and your cash flow |
| Evidence of the sale for tax and accounts | Your accountant and the department |
| The instrument that passes on input tax credit | Your buyer — this is why they care about the details |
That last job is the one businesses new to GST underestimate. A sloppy invoice is not just untidy: it can cost your customer the tax they paid you. See what is input tax credit.
Invoice, receipt, quote: not the same thing
| Document | Says |
|---|---|
| Quotation | "This is what it would cost." No obligation on either side |
| Proforma invoice | "This is what the bill will look like." Used for advances and approvals. Not a tax document |
| Tax invoice | "This was supplied. You owe this." The real document |
| Receipt | "You have paid." Acknowledges money, does not create a debt |
| Delivery challan | "These goods are moving." Accompanies goods where no sale has happened yet |
Which to issue when is a question in its own right — see tax invoice, bill of supply, proforma or challan.
GST Invoice Generator — free, no signupMake a GST invoice in your browser, download the PDF, no signup.When the invoice has to be issued
GST sets deadlines, and they are earlier than most businesses assume.
| Supply | Issue the invoice |
|---|---|
| Goods that move | Before or at the time the goods are removed for delivery |
| Goods that do not move | Before or at the time they are delivered to the buyer |
| Services | Within 30 days of supply (45 days for banks, NBFCs and insurers) |
The bill goes with the lorry
For goods, the invoice is supposed to exist before the goods leave — not be typed up at the end of the week. Goods moving without the right documents is a separate problem again; see what is an e-way bill.
What a billing process has to do
Producing a PDF is the easy part. A billing process that actually works has to:
- Number correctly — one unbroken series per financial year, never reused. See invoice numbering rules.
- Calculate tax correctly — the right rate per item, and the right split for the place of supply.
- Move the stock — what was billed has left the building, and the count should say so.
- Create the receivable — the bill should appear on a list of what people owe you, not just in a folder.
- Be findable — by number, by party, by date, in seconds, three years later.
- Be correctable — through a credit or debit note, not by editing history.
Why spreadsheets stop working
A spreadsheet handles the first two well enough and none of the rest. The failure is rarely dramatic; it is slow. Two people bill at once and reuse a number. Stock on the sheet stops matching the shelf. Nobody can say what a party owes without adding up a folder. By the time it is obviously broken, there are two years of records to untangle.
If you want to see how this looks when it is handled properly, create a GST tax invoice walks through it end to end.
Does an invoice have to be signed?
A tax invoice requires the signature or digital signature of the supplier or an authorised representative. A digitally signed electronic invoice satisfies this; an e-invoice with an IRN carries its own signature from the portal.
How many copies of an invoice for goods?
The rules describe three — original for the recipient, duplicate for the transporter, triplicate for the supplier. For services, two.
Can I email an invoice instead of printing it?
Yes. What matters is that it carries every required particular and reaches the buyer. Where goods are moving, the transporter still needs the documents the movement requires.
How long do I keep invoices?
GST record-keeping runs to 72 months from the due date of the annual return for that year, and other laws may require longer. In practice, keep them indefinitely — storage is cheap and a missing invoice is not.
Sources
- CGST Rules 2017, Rule 46 — particulars of a tax invoice
- CGST Act 2017, section 31 — time of issue
- CBIC — GST Acts, Rules and notifications (cbic-gst.gov.in)
Free tools for this
How TracEasy handles this
Related reading
GST invoice format: what must be on the bill
The fields Rule 46 requires, with a worked example of each.
Tax invoice, bill of supply, proforma or challan?
Five documents that look alike and mean completely different things.
Invoice numbering rules under GST
Sixteen characters, one unbroken series per financial year, never reused.