A proforma invoice looks almost identical to a real invoice — same layout, same line items, same total — but it is not a demand for payment. It is sent before the goods or work are delivered, to give the client a preview of what the final invoice will look like: for customs declarations on an international shipment, for a client who needs a firm number before releasing an advance payment, or simply to confirm final pricing before work begins.
A real invoice is sent after the goods or work are delivered (or, for milestone or deposit billing, after the agreed trigger is reached), and it is a genuine demand for payment with a due date and payment terms. This is the document that actually gets paid against and that a receipt can later reference.
The practical difference shows up in what each document is allowed to do: a proforma invoice is not recorded as revenue and does not go into accounts receivable, since no obligation to pay exists yet. A real invoice does both. Sending a proforma invoice and treating it as a real one — chasing payment against it, recording it as revenue — mixes up a preview with a bill.
A proforma invoice is typically superseded by a real invoice once the work is actually delivered or the shipment goes out — the numbers usually carry over unchanged unless something shifted between the preview and the delivery, in which case the real invoice reflects what actually happened.
Numbering matters here too: a proforma invoice should carry its own distinguishable numbering or a clear "PROFORMA" label, precisely so it never gets filed, paid, or reconciled as if it were the real invoice that follows it.
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