Quote vs Purchase Order vs Proforma Invoice vs Invoice: What's the Difference?
You receive a document labelled "proforma invoice." Is it a quote? An invoice? Do you need to pay? Are you committed? These four documents (quote, purchase order, proforma invoice, final invoice) circulate in every B2B transaction. They can look almost identical, carry the same totals, and yet they serve entirely different purposes and carry very different legal weight.
Mixing them up costs time and money. A purchase order signed when you thought you were approving a quote locks you into a commitment. A proforma invoice recorded in your accounting system as a real invoice distorts your books. This guide clarifies each document in plain terms, with a comparison table and the most common mistakes to avoid.
1. The quote (or quotation)
A quote is a detailed commercial proposal issued by the supplier. It describes the goods or services offered, their prices, and the terms of sale. Until the buyer signs it, only the supplier is bound: they commit to holding the stated prices for the validity period shown on the document.
Legal weight. Once the buyer signs a quote (often with a note like "approved" or "accepted"), it becomes a binding contract. Both parties are locked into the scope, pricing, and terms it contains. In many jurisdictions, specific categories of services (home repairs, removals, construction work) require a written quote by law once the value exceeds a threshold.
What it must include. Date, supplier identity (company registration number, address), detailed description of each line item, unit price excluding tax, applicable tax rates, total including tax, validity period, and payment terms.
Key takeaway. The quote is your reference document for comparing supplier offers. The entire consultation phase revolves around it. An unsigned quote does not commit you.
2. The purchase order (PO)
A purchase order is issued by the buyer, not the supplier. It is your formal act of purchase: you confirm that you accept the offer and are placing an order on the agreed terms.
Legal weight. A purchase order signed by the buyer and acknowledged (or confirmed) by the supplier constitutes a sales contract. It is legally as binding as a signed quote, sometimes more so, because it typically references the buyer's general terms and conditions of purchase.
How it differs from a signed quote. In practice, both can serve as the "contract." The difference is who issues the document: the quote comes from the supplier, the purchase order comes from the buyer. Large corporations and public-sector organisations require an internal PO before any purchase, even when a quote has already been signed. For a small business buying materials from a distributor, the signed quote alone is usually sufficient.
Key takeaway. If your supplier asks you for a "purchase order," it is your responsibility to issue it. The PO mirrors the quote (references, quantities, prices) and adds your internal order number, the confirmed delivery date, and your billing address.
3. The proforma invoice
A proforma invoice is an informational document that looks like an invoice but is not one. It has no accounting value and must never be recorded in your books as an expense.
What it's used for. The proforma invoice appears in three main situations:
- Customs and international trade. For clearing goods through customs, authorities need a document describing the nature, value, and origin of the goods before the final invoice is issued. The proforma serves this purpose and is standard in cross-border shipments.
- Financing applications. Your bank or a leasing company asks for a formal cost estimate for a purchase before approving a loan or lease. The proforma fills that role.
- Pre-order confirmation. The supplier sends a proforma to confirm the terms of an order before issuing the real invoice. This is common in international commerce, where the order must be approved by multiple departments before payment is released.
Legal weight. None, in an accounting or tax sense. A proforma invoice creates no obligation to pay. It does not replace the quote or the final invoice. If a supplier sends you a proforma and asks you to pay against it, that is either a terminology mix-up or a red flag.
Key takeaway. If you receive a "proforma invoice," do not pay it and do not book it. Wait for the final invoice.
4. The final invoice (commercial invoice)
The final invoice is the accounting and tax document issued by the supplier after delivering the goods or completing the service. It is the only document that triggers the obligation to pay and must appear in your accounting records.
Legal weight. An invoice is required for every transaction between businesses in virtually every jurisdiction. It serves as proof of the transaction, the basis for tax calculations (VAT, sales tax), and a key document in case of audit. Specific requirements vary by country, so always verify local rules.
Relationship to the quote. The invoice must match the signed quote or purchase order. If the invoiced amount differs from the agreed amount, you have grounds to dispute it. This is why archiving your signed quotes matters: they are your reference in case of a billing disagreement.
Comparison table
| Quote | Purchase Order | Proforma Invoice | Final Invoice | |
|---|---|---|---|---|
| Issued by | Supplier | Buyer | Supplier | Supplier |
| Legal weight | Contract if signed | Contract if acknowledged | None (informational) | Payment obligation |
| Accounting treatment | Not recorded | Not recorded | Not recorded | Expense + tax deductible |
| Can be modified | Yes, until signed | Yes, by amendment | Yes, freely | No (credit note required) |
| Primary use | Compare offers | Formalise the order | Customs, financing | Trigger payment |
3 common mistakes
Signing a proforma thinking it's a quote. A proforma is not a quote. If you sign it with "approved," the situation is legally ambiguous: you have expressed consent on a document with no clear contractual framework. To avoid trouble, always request a formal quote before signing anything.
Recording a proforma in your accounting system. Some accounting software does not differentiate between document types. If you enter a proforma invoice as a supplier invoice, you inflate your expenses and your deductible tax. Your accountant will have to reverse it. The rule: only the final invoice goes into your books.
Treating a signed quote as completely locked, with no room for adjustment. A signed quote binds both parties to the agreed scope, but modifications are still possible through a written amendment if both sides agree. The rigidity is in the relationship, not the document. If the scope changes, draft a written amendment rather than accepting a verbal change that will show up on the invoice.
Which document at which stage?
The normal flow of a B2B purchase follows this sequence: you send a pricing request to several suppliers. They each respond with a quote. You compare the quotes (this is where hidden fees surface). You sign the chosen quote, or you issue a purchase order that mirrors the quote's terms. The supplier delivers. They issue the final invoice. You pay.
The proforma invoice runs in parallel, never in the main flow. It serves as a supporting document for customs, banks, or internal approvals. If a supplier sends you a proforma where you expected a quote, ask for a quote. If you receive a proforma where you expected an invoice, ask for the final invoice.
FAQ
Can you cancel a signed quote?
In principle, no. A signed quote is a contract, and both parties are bound. In practice, cancellation is often negotiable if work has not started and the supplier has not incurred costs. Expect to compensate the supplier for any expenses already committed (materials ordered, staff allocated). The best approach is to negotiate a cancellation clause in the original quote.
Does a proforma invoice bind the supplier?
No. A proforma invoice is informational, not a contractual commitment. The supplier can change prices or terms between the proforma and the final invoice. If you need a firm price commitment, request a quote with an explicit validity period.
Do I need a purchase order for every purchase?
That depends on your organisation. Large companies and government bodies require one systematically. For a small business or sole trader, the signed quote serves as the order in most cases. The value of a PO is traceability: it creates a reference number that simplifies tracking, goods receipt, and invoice matching.
What if the invoice doesn't match the quote?
Dispute it in writing before you pay. Reference the signed quote number, identify the discrepancies line by line, and request a corrected invoice or credit note. You are not obligated to pay an amount higher than the signed quote, unless you agreed in writing to additional work or deliverables.
How long is a quote legally valid?
There is no universal statutory validity period. The validity is whatever the supplier states on the quote (30 days, 60 days, 90 days). If no period is mentioned, courts generally consider the quote valid for a "reasonable time," which depends on the industry and type of service. To avoid ambiguity, always insist on an explicit validity date.
Legal specifics vary by jurisdiction. Consult local counsel for binding advice.
Related reading:
- How to Compare Supplier Quotes: The Complete Guide
- 7 Hidden Fees Lurking in Your Vendor Quotes
- Supplier Price Request Email Template (Copy-Paste)
Once your quotes arrive, Quotal compares them line by line automatically, flags price gaps and hidden fees, and gives you a clear view before you place the order.