What to put on an invoice (and what gets it rejected)

A valid invoice needs eight things: a unique invoice number, the issue date, a payment due date, your business name and address, the client's legal name and address, an itemised description of what you supplied, the tax shown separately with its rate, and the total due with a way to pay it. Miss the number or the tax breakdown and an accounts team will usually send it back.

The first invoice I ever sent came back within an hour. Not because the amount was wrong — because I had written "web work, March" and nothing else. Their accounts payable person could not match it to a purchase order, could not tell which month's budget it belonged to, and could not see any tax treatment. It was a demand for money with no evidence attached.

The eight that are non-negotiable

1. A unique invoice number. Sequential, never reused. This is how payments get matched to documents, and in most tax systems it is a legal requirement, not a convenience.
2. The issue date. The date you raised it, which is usually what determines the tax period it falls into.
3. A real due date. "Due on receipt" is a payment term, not a date. Write the actual day.
4. Your business name, address and tax number — GSTIN in India, VAT number in the UK and EU, EIN in the US.
5. The client's legal entity. Not "Dave" — "Dave Morrison Joinery Ltd", with their address.
6. Itemised lines. What you did, quantity, unit rate, line total.
7. Tax shown separately, with the rate visible. Never folded silently into the total.
8. The total due and how to pay. Bank details, UPI ID, or a payment link.

The three that get invoices queried

Beyond the legal minimum, three omissions cause most of the back-and-forth.

No purchase order number. If your client issued a PO and your invoice does not carry it, a large company's system genuinely cannot route it for approval. It will sit in a queue until somebody manually intervenes, which can take weeks. Ask whether a PO exists before you invoice — it costs one message.

A vague description. "Consulting" is not a description. "Site survey and fault diagnosis, 14 March, 4 hours" is. The person approving the payment usually was not the person who hired you, and they need enough detail to believe the work happened.

A total that does not reconcile. If the line items add to 3,900 and the total says 4,100 because you silently added a call-out fee, the whole document loses credibility. Every number on the page should be derivable from the numbers above it.

What changes when you register for tax

Once you are registered — GST in India, VAT in the UK, and so on — the document usually stops being an "invoice" and legally becomes a tax invoice, with extra requirements. Typically: your registration number, the tax rate per line, the tax amount per rate, and in some jurisdictions specific wording like "reverse charge" for cross-border supply. The details vary enough by country that guessing is a genuinely bad idea — check your own tax authority, not a blog.

How long you have to keep it

Most countries want invoice records kept for five to seven years. India's GST rules say six years from the annual return; the UK says six years for VAT; the US IRS generally says three, longer in some situations. Whatever the number where you are, it is longer than the average phone lives — which is why the export matters more than people think.

What changes once you are tax-registered

Registration adds requirements rather than replacing them. In most systems the document must be identifiable as a tax invoice, carry your registration number, show the tax rate applied and the tax amount separately from the net, and give the total including tax. Several countries also require the customer's registration number above a threshold.

This matters to your customer more than to you: a business buyer normally cannot reclaim the tax without a valid tax invoice, so a document missing your registration number costs them money and comes straight back. What a tax invoice is covers the distinction, and the country pages cover what your own system demands.

The three that get invoices queried

Beyond the legal minimum, three omissions cause most of the back-and-forth.

A purchase-order number, where the customer uses them. Large organisations frequently will not pay without one, and the rejection is often automated and silent. Ask before you start work.

The right legal entity. Billing "Dave" when the contract is with "Dave Morrison Joinery Ltd" gives their bookkeeper a document they cannot enter. Ask for the registered name.

How to pay. An astonishing number of invoices omit bank details. If paying requires an email asking how, you have added days for nothing.

What does not need to be on it

A signature, in almost every jurisdiction — though convention differs. Your home address, if you trade from home and have a business address. The client's phone number. A logo, legally — though it changes how the document is received.

Terms and conditions in full do not belong on it either. A line referring to them is enough; the wall of text pushes the numbers onto a second page where nobody reads them.

Write lines a stranger can approve

The person who approves payment is often not the person who hired you. They are matching your document against a budget line or a purchase order, and they have no idea what "consultancy, September" refers to.

Compare these two:

Web work — £2,400.00

Website rebuild, phase 2 of 3: templates, CMS integration and content migration, per quote EST-0104 of 14 August — £2,400.00

The second is approved without a phone call. The first waits for one that nobody schedules.

Dates: there are two, and they differ

The issue date is when you raised it, and it usually determines the tax period it falls into. The supply date — when the work was actually done — can be different, and several tax systems require both when they differ. The due date is a third thing, and it must be a real date rather than "on receipt".

Currency and language

State the currency explicitly. "$4,100" is ambiguous across at least five countries; "USD 4,100" is not. If you are invoicing across a border, invoicing in a foreign currency covers which rate to use and what your own tax authority expects to see alongside it.

EstimateBill does this on your phone with no account and no internet — the invoice is built, the PDF is made and the record is kept entirely on the device. See how it works, or build one in your browser first.