Seven billing documents look nearly identical and mean entirely different things. Sending the wrong one causes real accounting and legal problems on both sides.
A quote is a fixed price you are committing to for defined work, normally with an expiry date. Once accepted, you are expected - and in many jurisdictions can be held - to honour it. An estimate is a considered approximation with room to move; the final bill can differ, within reason, and clients understand it that way. The words are not interchangeable, and using "quote" when you mean "estimate" hands the client a price commitment you did not intend to make.
A proforma invoice sits between agreement and billing: it looks like an invoice and states what will be charged, but it is not a demand for payment and not a tax document. Its legitimate uses are narrow and real - customs declarations for cross-border shipments, and clients whose process requires a document before they can raise a purchase order. A proforma does not belong in your invoice sequence and does not create tax obligations; the real invoice follows.
The invoice is the formal request for payment, and in accounting terms the document that creates the receivable. From the moment it is issued, your records show money owed, the payment terms clock is running, and in accrual-based tax systems the tax point has usually been triggered - which is why an invoice issued carelessly, too early, or twice is a genuine problem rather than a formality.
This is also why invoices are corrected with credit notes rather than edits. The issued invoice is an accounting event on both sides; the correction has to be an event too, or the two sets of books stop matching.
One consequence trips up new businesses: a document titled "Invoice" that was meant as a quote can be paid, booked as a payable, or - worse - queried by the client's auditors when the work never happened. Titles are read literally by accounting departments, because their systems and their obligations depend on them.
A receipt confirms money received. For invoiced work it is often skipped - the bank record and a "paid" status on the invoice serve - but clients paying in cash, and consumers generally, are entitled to expect one, and some jurisdictions require it. A receipt references the invoice it settles, the amount, the date, and the method.
A credit note is a negative invoice: it reduces or cancels an amount previously invoiced, carries its own number, and references the invoice it corrects. It is the correct instrument for overcharges, returns, agreed discounts after billing, and cancelled invoices. Refunding money without one leaves both ledgers claiming the client still owes, or you still owe, an amount nobody intends to pay.
A statement of account is a summary of everything open - invoices issued, payments received, balance outstanding - usually sent monthly. It requests nothing and creates nothing; it exists so a client with many invoices can reconcile. Sending statements as though they were invoices, or paying them as though they were, is a classic accounts-payable error worth guarding against with a clear "This is not an invoice" line.
| Invoice line item | Description | Example amount |
|---|---|---|
| Quote | A committed price for defined work. Expires. Becomes binding when accepted. | Before work |
| Estimate | A considered approximation. Final bill may reasonably differ. | Before work |
| Proforma invoice | Preview of a future invoice for customs or purchase-order processes. Not payable, not tax-relevant. | Before billing |
| Invoice | The formal demand for payment. Creates the receivable and usually the tax point. | At billing |
| Receipt | Confirms payment received against an invoice or sale. | After payment |
| Credit note | Negative invoice correcting or cancelling an earlier one. Own number, references the original. | On correction |
| Statement | Monthly summary of open invoices and payments. Not itself payable. | Periodic |
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