What to include on an invoice

An invoice does two unrelated jobs. It asks a person to pay you, and it is a tax document that has to survive somebody else's audit. The first job is why invoices get designed. The second is why they come back.

The failure is almost never the amount. It is a missing tax identifier, a date that contradicts another date, or a number that already appeared on an invoice three months ago. None of those stop a client from paying — they stop the client's accountant from booking it, which amounts to the same delay and a more embarrassing email.

The lines that are never optional

Wherever you invoice from, this is the core. If a line here is missing, the document is doing the first job and failing the second.

• Who you are: legal name, address, and your business or tax registration number in the form the register holds it.
• Who they are: the client's legal name and address — the entity, not the person who briefed you. Their tax number too, once either of you is VAT-registered.
• A unique invoice number, from a sequence that never repeats and never has a hole in it.
• The issue date, and separately the date the work was delivered when the two differ.
• What you did, in enough detail that a stranger can tell what was bought. "Consulting" is not a description.
• The amount, the tax rate applied, the tax amount, and the total — each on its own line rather than folded into one figure.
• The due date as a date, and the account details to pay it into.

Two of those are worth dwelling on, because they are where the arguments start.

The client's legal entity, not their brand

You were hired by a person, briefed over a call, and paid by a company whose registered name you have never seen written down. Invoice the brand and you have addressed a document to something that does not legally exist. Ask for the registration number once, at the start, and look the rest up in the public register — it takes a minute and it is the single most common reason an invoice is returned.

A description that survives a stranger

The test is not whether your client understands the line. It is whether an auditor, two years later, can tell what was supplied. "October retainer" fails that test. "Website maintenance, October 2026, 12 hours" passes it, and has the useful side effect of ending the conversation about what the retainer covered.

The numbering rule people get wrong

Invoice numbers must be unique and sequential. Most people know that. What catches them out is that the sequence cannot have gaps you cannot explain, which means you cannot delete an invoice you have already issued.

Sent the wrong figure? The fix is a credit note or a corrective document that references the original, not a quietly edited PDF and a re-send under the same number. The client's copy and yours have to stay identical, and once a document has left your hands, editing it in place breaks that.

The tax lines, and the one everyone forgets

If you are not registered for VAT, say so. An invoice with no tax line and no explanation looks like an invoice where the tax line was forgotten, and your client's bookkeeper cannot tell the difference. A single sentence naming the exemption you are using settles it.

If you are registered, the rate and the tax amount go on the invoice as separate lines from the net figure, and cross-border work needs one line more. Invoice a business in another EU country and the tax usually shifts to them under the reverse charge — which is only valid if both tax numbers are on the document and you have said which rule you are applying. Getting that wrong makes the tax yours.

• Domestic business client: your rate, your tax amount, both spelled out.
• Business client elsewhere in the EU: both VAT numbers on the invoice, no tax charged, and a line naming the reverse charge.
• Client outside the EU: usually outside the scope of your VAT, but the rule depends on what you sold and where the customer is.
• Private individuals anywhere: different rules again, and the one case where quoting a net figure will get you complaints.

When a shorter invoice is legal

Most tax regimes allow a reduced set of lines below a small-value threshold — the amount and the exact list vary by country, and the threshold is usually low enough that it covers a receipt rather than a project. It is worth knowing yours, because it is also the boundary above which every line in this post is mandatory.

For anything you would call client work, assume the full list applies. The simplified form exists for the coffee, not for the retainer.

The part that decides whether you get paid

Everything above makes the invoice valid. None of it makes it get paid. That comes down to three lines that are usually treated as an afterthought.

1. A due date as an actual date. "Net 14" asks the reader to do arithmetic, and the arithmetic gets done in your client's favour.
2. A payment reference, and the same one in your bank records. Without it, reconciling a payment against an invoice is manual work you will do every month forever.
3. One payment method, stated plainly. Offering three invites a decision, and a decision is a delay.

There is also a timing question nobody mentions: send it the day the work is accepted. An invoice issued two weeks late has already spent two weeks of its payment terms, and every day of that came out of your cash flow rather than your client's.

Keeping them, and the format question

You have to keep issued invoices for years — how many depends on your country, and it is longer than most people assume. Keep them somewhere that is not one laptop, and keep the version the client received rather than the record that generated it.

The bigger change is what counts as an invoice at all. Several European countries now require structured electronic invoicing rather than a PDF: Italy through its national system, Germany with a receiving obligation already in force and issuing phasing in by turnover, Poland through KSeF, Spain under Verifactu from 2027. A PDF is still fine in plenty of places and already illegal in others, which is a question about your own market and your client's, not about your invoice template.

Seven checks, one of which — the sequence — you should never be doing by hand. Numbering, dates and tax lines are exactly the fields software should be filling in, which is what makes a template in a word processor a bad place to keep them.