Purchase Order

A purchase order is the client's document, not yours, and the direction is the part people get backwards: you send invoices, the client sends purchase orders. A PO is issued by the buyer before the work happens, to authorise a specific spend — what they are buying, the quantities, the agreed prices, the delivery or performance dates, and a PO number their finance system uses to track the whole thing from approval to payment. For a freelancer or a small business, a PO arriving means the money has already been budgeted and signed off inside the organisation, which makes it the most reassuring document a large client can send you. What it is not is a guarantee of prompt payment, and it is not a description of the work in the detail a contract or a statement of work carries.

A typical purchase order carries the PO number, the buyer's bill-to and ship-to addresses, line items with quantities and unit prices, a total or a not-to-exceed amount, the delivery or service dates, the payment terms, the name of the person who approved it, and a block of standard terms and conditions — often incorporated by reference to a web page rather than printed on the document. Three of those matter more than the rest. The PO number is what gets your invoice paid. The amount is the ceiling you have to bill inside. And the terms block is the part nobody reads, which is usually where the payment terms you are actually on turn out to be written.

The reason the PO number is non-negotiable is that in any organisation large enough to have an accounts payable function, your invoice is not so much read as matched. AP compares three things: the purchase order that authorised the spend, an internal record that the work was received or approved, and your invoice. When the three agree, the invoice drops into the next payment run with no human involved. When they do not — no PO number on the invoice, an amount above what the PO authorised, a line description that does not resemble the PO's, a business name different from the vendor name on the PO — the invoice is set aside as an exception and waits for somebody to reconcile it by hand. That is the most common reason a large client's payment arrives a full cycle late, and none of it is personal; it is a rule inside a system.

Billing against a PO is mostly a discipline of matching. Quote the PO number exactly as the client wrote it, on the face of the invoice and in the email subject line. Keep your line descriptions recognisably close to the PO's lines rather than rewriting them in your own words. Never invoice above the authorised total: an invoice for more than the PO covers is not trimmed to fit, it is held. If the scope grows, get a revised PO or a change order in writing before you do the extra work, because approving a spend after the money has been committed is a slower process in most companies than approving it in advance. And if you are billing in stages against one PO, reference it on every invoice and make the running total easy to see, so the person matching invoice four does not have to add up the first three.

InvoiceBloom does not raise or track purchase orders — those come from the client's procurement system, not from an invoicing tool — and there is no separate PO field on an invoice. The two placements that work are a line description or the payment instructions block, both of which print on the invoice the client receives rather than sitting in the covering email, where a finance team will never see it.

Legally, a purchase order is usually best understood as an offer to buy on the terms it carries, which becomes an agreement when you accept it or start performing. The practical consequence is that the fine print attached to a PO can quietly replace what you negotiated: payment terms longer than the ones you quoted, an insurance requirement, an indemnity, a clause assigning ownership of your work, or a right to cancel at will. For goods, US commercial law has an entire doctrine about whose paperwork wins when two conflicting sets of terms cross in the post — the battle of the forms, under the Uniform Commercial Code. For services the argument is rarely that theoretical, but the defence is the same and it is cheap: read the terms before you accept, and if you already have a signed agreement, say in your acceptance that the PO is issued under it. One sentence when the PO arrives is worth more than a strong opinion six months later, and where the amount or the risk is real, have a lawyer read the terms rather than relying on a glossary.

Two variations surprise people often enough to be worth knowing. A blanket or standing purchase order authorises a ceiling over a period rather than a single job — forty thousand dollars of design work for the fiscal year, say — which you then draw down invoice by invoice. Nobody will tell you when you are approaching the ceiling, so track the remaining balance yourself; the client's system simply stops paying, and it tends to happen in the month you can least afford it. The other is expiry. Purchase orders frequently carry an end date tied to the client's fiscal year rather than to your project, and a PO that expires in the middle of a six-month engagement is a problem to raise in week one, not in month four.

Most small clients do not use purchase orders and do not need to; a signed proposal with clear payment terms does the same work. Ask about one when the payer is a company rather than a person, when the amount is significant, when you are billing a school district, hospital system, agency, government body or general contractor, or whenever the person hiring you is plainly not the person who releases money. The whole question is one line in the kickoff email — does this need a purchase order, and if so, who raises it? Asking before you start costs nothing; finding out after you have invoiced costs a payment cycle. If the client's approval process needs an invoice-shaped document before a PO can be raised, that is precisely what a proforma invoice is for. Public-sector payers add a layer of their own: US federal agencies pay against what the Prompt Payment Act calls a proper invoice, and the contract specifies the order or contract number it has to quote, so an invoice missing that reference is not paid late — it is returned.