Purchase order vs invoice: the difference
By Diljit Ramachandran, founder of The Invoice Generator. Published Oct 26, 2026.
A purchase order (PO) is a document a buyer sends to a seller to order goods or services. An invoice is a document the seller sends to ask for payment. The PO usually comes first and the invoice usually follows delivery.
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What is the difference between a PO and an invoice?
A PO authorizes the purchase; an invoice bills it.
| Purchase order | Invoice | |
|---|---|---|
| Issued by | Buyer | Seller |
| When | Before the work | Usually after delivery |
| Purpose | Says what to buy, at what price | Asks for payment |
| Lists | Items, quantities, prices | What was delivered and owed |
| Other side | Fills the order | Matches it to the PO and pays |
Which comes first?
The usual order is: quote, purchase order, delivery, invoice, payment, receipt. A proforma invoice may come before or after the PO. To write one, see how to make a purchase order.
Why do companies ask for a PO?
A PO gives them control and budget approval. Many companies, especially larger ones, match the invoice to the PO and the delivery record, a three-way match, before they pay. Put the PO number on your invoice.
Can you invoice without a purchase order?
Yes, if the client does not require one. If a client needs a PO, ask for it before you start work or deliver.
Questions
- Can a purchase order be used as an invoice?
- No. A PO is the buyer's order. It does not ask for payment, so you still send an invoice. A purchase order generator makes the PO side.
- Should the invoice match the PO?
- Yes. Use the same items and prices. If the price or quantity changed, ask the buyer to amend the PO, because a mismatch is what stalls payment.
Keep every document in one place
- A free account saves a copy of each invoice, remembers your clients and items, and shows what is paid and overdue.
- Pro numbers your invoices for you, emails payment reminders, and repeats the ones you send every month.
Drafted with AI assistance from public sources and our own tool, and published by Diljit Ramachandran. It has not been checked by an accountant. It is general information, not tax or legal advice. Rules differ by place; check with an accountant or your local tax office.