An invoice has one job: to be paid without a conversation. Here is what belongs on it, what causes delays, and the small details that decide whether it goes into the payment run or into a pile.
An invoice needs eight things: who you are, who they are, a unique number, the date, what the work was, what it costs, what tax applies, and how to pay you. Miss any of them and somebody has to ask a question, and every question adds a week.
That is the whole test. Not whether it looks professional — whether the person who processes it can process it without contacting you.
Rarely because the client will not pay. Usually because the invoice made it easy not to.
The person who receives it is not the person who commissioned the work. It goes to accounts, where somebody who has never heard of the job has to match it against a purchase order, code it to a budget, and get it approved. If anything is missing or ambiguous, they do not investigate. They set it aside and move to the next one.
Three specific things cause most of it. No reference the client can match — no purchase order number, no job name they recognise. A description so vague that the approver cannot tell what they are approving; "consultancy services" tells them nothing and invites a query. And payment terms that are absent, so the invoice joins the default queue, which is always longer than the one you would have chosen.
None of these are disputes. They are administrative friction, and they cost weeks.
Your details and theirs. Your business name, address, contact, company and tax registration numbers where you have them. Their full legal name and address, not the trading name on the shopfront — accounts systems match on the legal entity.
A unique number, in a sequence. This is not bureaucratic; it is how both sides find the invoice again, and in most jurisdictions sequential numbering is a legal requirement.
Dates. The issue date, and separately the due date as an actual date. "Net 30" makes the reader do arithmetic. "Due 14 October" does not, and a specific date is harder to let slip.
A description that means something to them. Not what you did — what they asked for. Include their reference, the job name, the site, the period covered.
The amounts, itemised. Quantity, rate, line total, subtotal, tax, total. Show the tax rate and amount separately even where it is zero, and say why it is zero if it is.
How to pay. Account details in full, including whatever international format applies if they are abroad. Every extra step here is a delay.
And one line most people leave off: what happens if it is late. Stating your statutory or contractual right to interest changes nothing when everyone behaves, and changes a great deal when they do not.
Two invoices for the same work, same client, same amount.
The first says "Consultancy — March" with a total and a bank account. It arrives in accounts, nobody can match it to a budget, it waits for somebody to ask the manager, the manager is away, and it is paid seven weeks later.
The second says "PO 4471 — site survey and report, Riverside unit, 2–6 March", with the line items, the tax shown separately, and a due date. It matches automatically, goes into the next payment run, and is paid in eighteen days.
Nothing about the relationship differed. One of them was simply easier to pay than to set aside.
How soon should I send it?
Immediately on completion, or on the agreed milestone. An invoice sent three weeks late signals that you are not counting, and gets treated accordingly.
What payment terms should I use?
Whatever you agreed before starting. If nothing was agreed, thirty days is the common default; shorter is normal for small jobs. The important part is that it was agreed in advance rather than announced on the invoice.
Should I ask for a deposit?
For anything substantial, yes, and take it before the work starts. A client who will not pay a deposit is telling you something, and it is cheaper to hear it then than at the end.
Do I need software?
Not until the volume justifies it. A spreadsheet that numbers itself, calculates totals and tax, and produces a clean document handles a great many businesses for years.
What if it is not paid?
Chase early and in writing, politely, with the invoice attached. Most late payment is administrative, and a reminder at day thirty-one resolves most of it. Keep the escalation for the ones that survive two reminders.
The KISS Invoice Template is a spreadsheet that does the arithmetic — line totals, subtotal, tax and total — and lays the whole thing out so nothing on the list above is missing. Fill in your details once and reuse it. Five euro, one file, no subscription.
See the templates →