What Is the Difference Between Purchase Order Vs Invoice

Purchase Order Vs Invoice: Key Differences Explained

A purchase order (PO) is a buyer-issued document that formally requests goods or services from a supplier. At the same time, an invoice is a supplier-issued document that requests payment after delivery. Though both are part of the same transaction, a PO approves the purchase and an invoice records the amount due. Confusing them can lead to payment delays and accounting issues.

How are a purchase order and an invoice different?

The clearest way to understand the difference is to compare who creates each document, when it is issued and what purpose it serves in a transaction.

Aspect	Purchase order	Invoice
Issued by	Buyer	Seller
Sent to	Supplier or vendor	Buyer or client
Purpose	To place an order and commit to payment	To request payment for goods or services delivered
Timing	Before delivery	After delivery (or as agreed)
Legal status	An offer from the buyer	A demand for payment from the seller
What it contains	Item descriptions, quantities, agreed price, delivery terms	Items delivered, amounts due, tax breakdown, due date
Reference number	PO number	Invoice number (often references the PO number)

Which document comes first in a transaction?

The PO comes first in a standard business-to-business (B2B) transaction. The usual sequence is:

The buyer creates a PO and sends it to the supplier.
The supplier reviews, accepts or negotiates the PO.
The supplier delivers the goods or services as agreed.
The buyer checks and accepts the delivery.
The supplier issues an invoice, usually referencing the PO number.
The buyer matches the invoice with the PO and processes the payment.

Can a business skip the purchase order and go straight to an invoice?

Technically, yes. Many small businesses and informal transactions skip the PO stage, in which the supplier delivers the goods or services, and issues an invoice directly. This approach may work when the transaction value is low, the relationship is trusted and the risk of disputes is minimal.

However, skipping a PO can create issues in larger or more structured transactions. Without a PO, there is no formal record of agreed prices, quantities or delivery terms. If the invoice does not match the original agreement, resolving the dispute can become challenging.

Under GST, an invoice is mandatory for taxable supplies, but a purchase order is not a statutory requirement. However, many businesses and buyers use POs as internal controls and as a condition for processing payments.

Conclusion

A purchase order and an invoice are not interchangeable. They serve different roles at different stages of a transaction. The PO sets expectations before the purchase, while the invoice records the final amount due after delivery. Keeping both documents accurate and matched helps businesses avoid payment delays, disputes and compliance issues.

With TallyPrime, businesses can create, track and reconcile purchase orders and invoices in one place, simplifying and improving transaction management.

Is a purchase order legally binding?

A PO becomes legally binding once the supplier accepts it, either in writing or by commencing fulfilment of the order. Before acceptance, it is considered a buyer's offer and can generally be withdrawn. After acceptance, both parties are bound by its terms.

What happens if the invoice amount does not match the PO?

This is known as an invoice discrepancy. The buyer usually pauses payment and raises a query with the supplier. The supplier must issue a revised invoice or explain the difference. Under Goods and Services Tax (GST), changes in taxable value or tax amount may require a credit note or debit note.

Does a purchase order need to have a GST number?

No, a PO is not a GST document, so there is no statutory requirement for it to include a GSTIN. However, adding both parties’ GSTINs is good practice as it helps tax invoice processing and reconciliation.

Can one invoice cover multiple purchase orders?

Yes, a supplier can combine multiple POs into one invoice if both parties agree. The invoice should mention all relevant PO numbers so the buyer can match each item to the correct order. This is common in long-term vendor relationships with periodic billing.

What is the difference between a proforma invoice and a tax invoice?

A proforma invoice is a preliminary document shared before delivery to provide an estimated cost. It is not a payment request and does not create a GST liability. A tax invoice is issued after supply by a registered supplier and is a statutory document under the CGST Act.

Is the purchase order number mandatory on a GST invoice?

No, the Central Goods and Services Tax (CGST) Act does not require a PO number on a GST tax invoice. However, many buyers ask for it as part of their payment process and including it makes invoice matching and audits easier.

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