A plain explanation of due invoice — what it is for, who issues it, what goes on it, and what happens if the wrong one is used.
What every one of them has in common
Whichever document it is, three things apply. It needs a consecutive serial number unique within the financial year, of not more than sixteen characters and using only letters, numbers, hyphens and slashes. It needs identifying content for both parties. And it has to be retained for the prescribed period, which is counted from the due date of the annual return rather than from the date on the document.
Each document type also needs its own series. A proforma numbered in your tax invoice series is a genuine problem, because it consumes a number from a series that has to be consecutive and complete.
Rates, turnover thresholds, e-invoicing applicability and the time limits for issuing all change. Nothing on this page states one as a current fact — check the notification in force for your own circumstances.
Overdue, pending, due — and why the invoice cannot tell you
These words describe a state rather than a document. The invoice is the same invoice; what changes is whether it has been paid, and that is information no copy of the invoice contains.
Which is the whole problem with running billing out of files. A folder of PDFs or a spreadsheet of invoices can tell you what you billed. It cannot tell you what is unpaid, how long it has been unpaid, or which customer accounts for most of it — not without someone sitting down and reconciling receipts against invoices by hand.
What answers the question is a receivables position: every invoice with its payments applied, aged into buckets, per customer. Then "what is overdue" is a screen rather than an afternoon, and the conversation with a customer has a number in it.
Two things make collection measurably better and neither is chasing. Payment terms and a due date printed on the invoice, so the date was agreed rather than assumed. And a reminder that goes out on a schedule rather than when someone remembers. Both are the kind of thing a system does and a file cannot.
Issuing these properly, free
- Tax invoices with the complete prescribed field set, tax split per line.
- Bills of supply for exempt and composition supplies, with no tax line.
- Proformas and quotations in their own series, converting to an invoice without retyping.
- Credit and debit notes that reference the original invoice rather than editing it.
- Separate consecutive series per document type, issued centrally so a number cannot repeat.
- Tax derived from the place of supply, so CGST/SGST against IGST is never a judgement call.
- A receivables position — what is unpaid, how old, and whose.
- Export of everything to CSV, Excel and JSON, on every plan.
- ₹0 on the free plan, no card, no expiry.
Setting up your document series
- Start free now — email and password, no card.
- Enter your business name, address and GSTIN once.
- Set the next number for your tax invoice series, carrying on from whatever you last issued.
- Give proformas and quotations their own prefix, so they can never consume an invoice number.
- Do the same for credit notes and for bills of supply if you make exempt supplies.
- Add your customers with their GSTINs, and your items with HSN or SAC codes and rates.
- Raise one of each document you actually use, and check the numbering behaved as you expected.
The numbering series, which is where most of this goes wrong
The rule is short: a consecutive serial number, unique within the financial year, not more than sixteen characters, made only of letters, numbers, hyphens and slashes. One series, or clearly separated series where you genuinely need more than one — each consecutive in itself.
A file cannot enforce any part of that. The number is typed, which means it can be repeated, skipped, or quietly rolled back when yesterday's invoice is edited into today's. Nothing notices.
The half that is forgotten is cancellation. A cancelled invoice keeps its number and stays in the series as cancelled. Deleting the row and reusing the number leaves a gap in your books and a figure in your customer's, and reconciling those two is a long afternoon with a bad outcome.
Separate series per document type is the other discipline. Proformas, credit notes and bills of supply each need their own, and mixing them is how a tax invoice series ends up with holes in it.
Timing: when the document has to exist
Issuing the right document late is its own problem, separate from issuing the wrong one. The time of supply decides when tax becomes payable, and the invoice date is one of the inputs to it — so an invoice raised whenever it is convenient can move a liability into a period you have already filed.
The limits differ by what is being supplied. For goods the trigger is tied to removal or delivery; for services it is tied to completion of the supply, within a prescribed number of days. Continuous supplies, supplies on approval and reverse-charge supplies each have their own rule.
The practical version of this is unglamorous: raise the invoice when the supply happens, not when the customer asks for it, and not in a batch at month end because that is when someone has time.
These limits have been amended before. Check the one applying to your type of supply rather than relying on a remembered number of days.
CGST, SGST and IGST — worked out, not chosen
Whether a sale attracts CGST and SGST or IGST is not a preference. It follows from the place of supply: same state as your registration means the tax splits into central and state halves, a different state means one integrated tax at the combined rate.
That sounds simple and goes wrong constantly, because it is a dropdown in most billing software and a dropdown is something a tired person clicks past. In Billixo the split is derived from the state on the customer record against the state on your registration, and it changes the moment either does.
The consequence of getting it wrong is real: an IGST invoice raised as CGST/SGST has to be credited and reissued, and if the return has already gone in, amended.
HSN and SAC codes, and how many digits you need
Every line on a tax invoice needs an HSN code for goods or a SAC for services. How many digits depends on your aggregate turnover in the preceding financial year — smaller businesses report fewer digits than larger ones, and B2B and B2C invoices are treated differently.
Because the requirement is tied to turnover and has been tightened in stages, the practical answer is to store the fullest code you can against each product once, and let the software report at the level required. A six-digit code can always be truncated; a two-digit one cannot be expanded.
Billixo keeps the code on the product record and carries it onto every line automatically, and its AI HSN lookup will suggest one from a plain description when you genuinely do not know.
Bill scanning, in practice
The single largest time cost in most small businesses is not raising invoices — it is entering purchases. A photograph of a supplier bill goes in and a structured draft comes out: supplier, GSTIN, line items, rates, tax split and total.
You check it. That is the workflow, and it is deliberate: an extraction you did not read is a liability, not a saving. But checking a filled form takes fifteen seconds and typing one takes three minutes, and that difference compounds over a month of purchases.
Who it is built for
Small and mid-sized Indian businesses that are registered under GST and bill regularly. One person doing everything, or a counter with three people billing at once and an accountant who needs the month to close cleanly.
The design assumption throughout is that whoever raises the invoice is busy and is not a tax specialist. So the tax is computed rather than asked for, the compliance fields are populated rather than presented as questions, and the report the accountant wants is a download rather than a request.
Try it free — the free plan needs no card and does not expire.
The price, plainly
Free is ₹0 and stays ₹0. The paid plans are bought for a fixed term, paid once, with no auto-renewal and no card kept on file — when a term ends the account drops back to Free until you decide to buy again.
There is no per-invoice charge, no per-user surprise on the free plan, and no feature that is technically included but practically throttled. What the plan says you get is what you get.
Compare the plans on the home page, or just start free now and look at the ceiling from the inside.
Reliability, backups and getting your data out
Cloud billing software is only as good as its worst day. Two things matter more than any feature list: that your data is backed up somewhere you can reach, and that you can export it in a format something else can read.
Exports here are CSV, Excel and JSON, on every plan including the free one, covering customers, products, invoices and payments. That is the honest test of whether software respects you — not what it promises, but what it lets you take when you leave.
Frequently asked questions
What happens if I cancel an invoice?
The number stays with it and the invoice remains in the series marked as cancelled. It is not handed back for reuse — reusing it leaves a gap in your records and a figure in your customer's.
When do I have to issue a self-invoice?
Where you receive a supply attracting reverse charge from an unregistered supplier, there is no supplier invoice, so you raise one yourself for that inward supply in its own series. Which supplies attract reverse charge has been changed by notification, so confirm the current position.
Is a VAT invoice still valid in India?
VAT was replaced by GST in July 2017, so for an Indian supply today the document is a GST tax invoice. VAT is still live in other countries, which is usually why the term comes up — if you are exporting, that obligation belongs to the buyer's jurisdiction, not on your invoice.
Is it really free?
Yes. The Free plan is ₹0, needs no card and has no expiry. It has volume limits and leaves out the paid conveniences — watermark-free PDFs, GST return exports, the AI features, extra logins — but the invoices it produces are real GST invoices, and you can export your data from it whenever you like.
Do I need to install anything?
No. It runs in a browser, on a laptop, desktop or phone, so there is nothing to install, nothing to update and nothing tied to one machine. If the office computer dies, you sign in from another one and everything is there.
See it working on your own bills
The fastest way to judge billing software is to bill with it. Photograph one supplier invoice, raise one sales invoice, and look at the PDF your customer would receive.
Open the software demo → — free account, no card, about a minute to set up.
More details on the home page → — what it does, what it costs, and where the limits are.
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