How to invoice so you actually get paid

An invoice is not a request. It is a document that either matches what the other side's accounts system expects, or sits in a queue while somebody works out what to do with it. Most late payments are not disputes. They are mismatches.

What has to be on it

• The word Invoice — an untitled document is not obviously payable.
• A unique invoice number, and the customer's PO number if they gave you one.
• The date issued, and the date payment is due as a date rather than “30 days”.
• Your full business details, and theirs.
• Itemised lines: what, how many, at what unit price.
• Tax shown separately, and the total.
• How to pay — account details, or the payment link.

The PO number is the whole game

If your customer raised a purchase order, their accounts payable does three-way matching: the order, the delivery note, and the invoice. All three need the same number. An invoice arriving without it cannot be matched, so it does not get approved, and nobody tells you — it simply does not get paid until you chase.

Most invoices are not late because someone decided not to pay. They are late because nobody could work out which order they belonged to.

Terms that work

Put a real date, not a duration. “Due 8 September” is a deadline; “net 30” is a puzzle that starts from a date the reader has to find. If you take card or bank transfer, put the details on the invoice itself rather than in the covering email, which will not be forwarded to whoever pays it.

Invoice the day the work is done. An invoice sent three weeks late signals that the money is not urgent to you, and it will be treated accordingly.

The penny problem

If your line items do not sum to your total, the invoice looks careless before anyone reads a word of it. That happens when amounts are held as decimal fractions and rounded at display time — each line rounds independently, and the sum of the rounded lines is not the rounded sum. Holding money in whole cents from the start makes the arithmetic exact.

Keep the record

A browser tool that stores nothing cannot keep your register. That is a real limit, honestly stated: keep the PDFs somewhere consistent, or move to an accounting system once you are sending more than a handful a month. The register matters more than the document.