Invoice, receipt, quote or purchase order: which to send when

You agreed a price with a customer, did the work, and now you are staring at your software wondering whether to send an invoice, a receipt, a quote or a purchase order. They look almost identical on the page, the same logo, the same list of items and prices, which is exactly why people mix them up. The difference is not the layout. It is where each one sits in the deal.

TL;DR: A quote offers a price before the work. A purchase order is the buyer accepting and ordering it. An invoice requests payment once the work is done. A receipt confirms the payment was made. Same items, four different moments.

A quote offers a price before any work starts

A quote is the first document in the chain. You send it to a prospective customer to say “here is what this will cost”, before anyone has committed to anything. It lists the work or goods, the price for each line, and usually a date the price is valid until. Its job is to win the work and set expectations, so there are no arguments about cost later.

The word matters here. A quote is normally a firm price you will stand behind, while an estimate is your best guess that may move as the job becomes clearer. Both use the same layout, so spell out which one you mean in the notes if there is any doubt. A “valid until” date protects you, because it stops a customer accepting a months-old price after your own costs have changed.

A purchase order is the buyer accepting and ordering

A purchase order, or PO, flows the other way. The buyer sends it to you to formally request the goods or services at the agreed price. It carries a unique PO number and lists exactly what is being ordered. Where a quote says “here is what it would cost”, a purchase order says “yes, supply this”.

Not every deal needs one. A freelancer working with an individual rarely sees a PO at all. But larger organisations use them to control and approve spending internally before any money is committed, and they expect that PO number to appear on your later invoice so the two can be matched. If a client asks for your invoice to quote their PO, this is why.

An invoice requests payment once the work is done

The invoice is the document most people picture. You send it after the work is delivered to ask for payment, and it is the one that should leave no room for confusion. A clear invoice carries your details and the customer’s, a unique invoice number, the issue and due dates, an itemised list with quantities and rates, any tax, the total owed, and how to pay.

Numbering is the part people overlook. A simple running sequence such as INV-0001, INV-0002 keeps every invoice unique and in order, which matters for your own records and for tax. Some businesses fold in the year or a client code, like 2026-014. The scheme is yours to choose, as long as no two invoices ever share a number.

A receipt confirms the payment was made

A receipt is the last link in the chain. Once the customer has paid, you give them a receipt as proof the money was received. It shows who issued it, who paid, the date, what was paid for, the amount, and ideally the payment method. Where an invoice asks, a receipt confirms.

This is the document that matters most for payments with no card slip behind them, cash and bank transfers especially. A dated receipt gives both sides a record they can keep, which heads off the awkward “did you ever pay me for that” conversation. For rent, deposits and one-off charges, it is often the only proof either party will hold.

Reading the chain in order

Lined up in the order they travel, the four stop being interchangeable: quote, purchase order, invoice, receipt. The first two happen before the work, the last two after. The first and third are about agreeing and asking; the second and fourth are about accepting and confirming. Once you can place a document in that sequence, picking the right one is almost automatic.

If you raise these documents by hand, the invoice and billing tools build each of the four from one form, with your logo and a clean PDF, so the layout stays consistent and only the purpose changes.