Proforma Invoice vs Purchase Order: Differences and Order

A proforma invoice and a purchase order are opposite sides of the same deal. The seller issues the proforma invoice first as a formal quote showing what the goods will cost; the buyer then issues the purchase order to accept those terms and place the order. The proforma estimates and proposes; the purchase order commits and, once accepted, becomes a binding contract.

Last updated July 2026.

These two documents look almost identical on paper. Both list the goods, quantities, unit prices, and a total, and both are dated and numbered. The difference is who sends which, and what each one legally does. Getting them mixed up leads to the classic accounts payable problem: a proforma invoice keyed in as a real bill, paid before anything ships, with no purchase order to match it against.

Proforma invoice vs purchase order: the core difference

A proforma invoice is sent by the seller to the buyer as a good-faith estimate before a sale is finalized. A purchase order is sent by the buyer to the seller to formally order goods at agreed terms. In short, the proforma invoice is the offer to sell and the purchase order is the offer to buy that closes the deal.

Which comes first, the purchase order or the proforma invoice?

In most B2B transactions the proforma invoice comes first. The buyer requests a quote, the seller responds with a proforma invoice that fixes the price, quantity, and delivery and payment terms, and the buyer reviews it. Once the buyer is satisfied, they issue a purchase order that references and accepts those terms, which is the point the deal becomes firm.

That order is not universal. When a buyer already has a contract or a catalog price, they may send the purchase order first and skip the proforma entirely. Proforma invoices show up most often in first-time deals, custom orders, international shipments that need a document for customs and payment, and any sale where the buyer wants advance payment reassurance before committing.

Is a proforma invoice legally binding?

A proforma invoice is generally not legally binding on its own. It is a preliminary document, closer to a detailed quote than a contract, and its figures can still be negotiated or revised. It does not create an accounts payable entry and should never be paid as if it were a final invoice. The binding commitment forms when the buyer issues a purchase order that the seller accepts, which under US contract law creates an enforceable agreement.

Proforma invoice vs commercial (final) invoice

Do not confuse a proforma invoice with the commercial invoice that comes at the end. The proforma is an estimate sent before shipment. The commercial invoice is the real bill sent after the goods ship or the work is done, and it is the document that legally requests payment and gets booked in accounts payable. A clean order follows this sequence: proforma invoice, then purchase order, then delivery, then the final invoice that closes out the purchase order to invoice process.

How the documents flow in a real order

Here is the typical B2B sequence from first contact to payment, so you can see where each document sits:

1. The buyer asks a supplier for pricing on a set of goods.
2. The supplier replies with a proforma invoice quoting price, quantity, and payment and shipping terms.
3. The buyer reviews, negotiates if needed, and issues a purchase order accepting the terms.
4. The supplier confirms the purchase order and ships the goods.
5. The supplier sends the final commercial invoice, which the buyer matches to the purchase order and receipt before paying.

Both the proforma and the final invoice often arrive as a PDF or an email attachment, which means someone has to read the line items off the document and key them into the accounting or ERP system. You can skip that by having the tool above turn the document into structured header and line-item data, or by using an automated way to pull those fields straight out of an emailed attachment so nothing gets retyped. For inbound purchase orders specifically, upload the PO above and get the fields back as Excel, CSV, or JSON.

When should you use a proforma invoice?

Use a proforma invoice when a buyer needs to see committed pricing before they can raise a purchase order, when you require advance or partial payment, or when a shipment needs a value document for customs or a letter of credit. It gives the buyer everything they need to approve internally and cut a purchase order, without either side treating it as a final bill. If you sell on credit and want to shorten the gap between shipping and getting paid, pair clear terms with an automated way to follow up on unpaid invoices so the final invoice does not sit past due.

Frequently asked questions

Is a proforma invoice the same as a purchase order?

No. A proforma invoice is issued by the seller as an advance estimate of what the goods will cost, while a purchase order is issued by the buyer to formally place the order. They flow in opposite directions and serve opposite roles: the proforma proposes the sale, the purchase order commits to buying.

What comes first, a purchase order or a proforma invoice?

The proforma invoice usually comes first. The seller sends it to quote firm pricing and terms, and the buyer then issues a purchase order to accept them. The exception is when a buyer with an existing contract or catalog price sends the purchase order first and no proforma is needed.

Can you pay against a proforma invoice?

You can send an advance payment against a proforma invoice when both sides agree to prepay, but it should not be booked or paid as a normal accounts payable invoice. It is not a formal demand for payment. The final commercial invoice, issued after the goods ship, is the document that officially requests payment and gets recorded.

Does a proforma invoice have a purchase order number?

Often not, because the proforma usually predates the purchase order. Once the buyer issues a PO, later documents such as the order confirmation and the final invoice should carry that PO number so accounts payable can match the invoice to the purchase order and the goods receipt during three-way matching.

Why do sellers send a proforma invoice?

Sellers send a proforma invoice to give the buyer firm numbers to approve and raise a purchase order against, to secure advance payment where needed, and to provide a value document for customs on international shipments. It reduces back-and-forth by putting the full quote, quantities, and terms in one document before any commitment is made.