Definition
An invoice is the formal request for payment a seller issues to a buyer after delivering goods or services. It identifies both parties, lists the items or work supplied, breaks out tax, states the total, and tells the buyer where and by when to pay. In most jurisdictions, an invoice is also the underlying record for VAT or sales-tax reporting and the document a tax authority will ask to see in an audit.
Invoices come in several shapes — pro forma (issued before delivery as a price commitment), commercial (the standard payable invoice), credit note (a negative invoice that reverses or partially reverses a prior one), and self-billed (where the buyer issues the invoice on the seller's behalf under an agreement). For most small-business work, the standard commercial invoice is what people mean when they say 'invoice'.
Why it matters
An invoice does three jobs at once: it asks for money, it records the transaction in your books, and it acts as your evidence if the sale is ever disputed. A weak invoice — missing fields, vague descriptions, no due date — undermines all three jobs and is the most common reason a sale takes weeks to convert into cash.
Where this appears in your tools
The Invoice Generator builds invoices with the required fields, sequential numbering, and tax breakdowns. The Late Payment Recovery tool uses the invoice's due date to time reminder cadence, and the Profit Leak Analyzer reads invoice totals to surface revenue against costs.
Example
Studio Doe issues invoice INV-0042 on 1 March to Acme Ltd: one line ('Brand identity design — Phase 1 of 2, £2,400'), VAT at 20 percent (£480), total £2,880 GBP, due 15 March, payable by bank transfer. The document is the seller's request for payment, the buyer's basis for approval, and both parties' record for the books.
Common confusion
An invoice is not the same as a receipt. The invoice is issued before payment and asks for it; the receipt is issued after payment and confirms it. Many small businesses use the words interchangeably, which causes problems with refunds and tax records when one is needed and the other was sent.